The science behind how babies and toddlers sleep
Erin-Flynn Evans, PhD, MPH
Sleep scientist and co-founder of Baby Sleep Science

One of the most important contributors to a baby’s physical and psychological development is sleep. The same goes for their parents! But what exactly is the science behind how babies and toddlers sleep, and how does sleep – or a lack thereof – affect a little one’s waking hours, too? Dr. Erin Flynn-Evans is a sleep scientist and co-founder of Baby Sleep Science, an organization that offers families resources and help with children’s sleep. She spent more than 10 years working in the Division of Sleep Medicine at Harvard Medical School and at Brigham and Women’s Hospital. Dr. Flynn-Evans joins us to share how much sleep babies and toddlers should be getting, the most common challenges parents face regarding their baby’s sleep, and advice and tips for the whole family on how to catch some healthy and restorative ZZZs.


Listen to this episode to learn:

  • Sleep guidelines for infants and toddlers established by the American Academy of Sleep Medicine
  • The importance of naps – how frequently and how long should babies be napping as they grow?
  • How to optimize your baby or toddler’s sleep environment (make sure it’s cool, quiet, dark, and comfortable)
  • Signs to look out for signaling that your baby isn’t getting enough sleep
  • How to adjust your child’s sleep schedule to accommodate new school schedules and seasonal time shifts
  • How AI and mobile apps, like Huckleberry, can help you and your baby get better sleep
  • Resources for parents who need help with their child’s sleep


For more information, visit https://www.babysleepscience.com/.


Click here to read the full episode

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Full Transcript

The science behind how babies and toddlers sleep

Intro: Welcome to the Equal Parts Podcast brought to you by Care@Work.

Emily Paisner: Being a working parent is hard and it's even harder when you're sleep deprived because your baby isn't sleeping enough. Our guest today is Dr. Erin Flynn-Evans. She's worked at the Division of Sleep Medicine at Harvard Medical School and at Brigham Women's Hospital. She's now the Co-Founder and Sleep Scientist at Baby Sleep Science, an organization that offers families resources and help with their children's sleep.

In this episode, Erin and I talk about the science of sleep and how it affects babies and toddlers. We discuss what a normal sleep pattern should be for your little one nap time and everything in between. Have a listen. Erin, thank you so much for being here today. We really appreciate you joining us.

Dr. Erin Flynn-Evans: Thank you for having me.

Emily: Let's start by talking about babies and the science of sleep since that's your area of expertise. Can you tell us how sleep contributes to a baby's physical and psychological development?

Dr. Erin Flynn-Evans: We know babies are growing and developing every day and sleep is a really important part of that. It really touches every aspect of a baby's development. Growth hormone is produced during sleep so as baby grows physically, a large part of that is happening during sleep. Then as a baby learns how to interact with the world, observes new faces, and has new experiences, memory consolidation is happening during sleep. Language acquisition is being stored during sleep and motor skill memory is also something that's really tightly tied to sleep. As babies learn to roll over and crawl and then ultimately walk and run, sleep has a really important role to play there as well.

Emily: What's normal, if you will, in terms of sleep needs and patterns by age? Can you give us just a brief overview of from infants through toddlerhood and even when they're four or five years old, what is "normal"?

Dr. Erin Flynn-Evans: The American Academy of Sleep Medicine put out a series of pediatric sleep recommendations in 2016. That's a great reference for a parent who is looking for just what the professionals recommend. In general, when you have a newborn, they're going to sleep probably 14 to 16 hours a day without a really discernible pattern. Around six months, that will change and a baby will start to sleep somewhere between 10 and 12 hours overnight and have two or three naps during the day. Two of those naps are usually an hour or more.

By around the nine-month mark, most babies are just taking two naps and nighttime sleep stays around the 10-hour to 12-hour mark. Around 15 months, usually a range between 12 and 18 months, babies will drop one of the two naps and just have a single anchor nap in the middle of the day. Then at around age three, they'll drop that nap. I would say three is the minimum age they should drop the nap. We'll have a single night of somewhere between 10 hours and 13 hours of sleep. That single night of sleep lasts with that pretty stable pattern of 10 hours to 13 hours all the way through about age six.

Emily: What if your child isn't getting that amount of sleep? Should parents be concerned about that?

Dr. Erin Flynn-Evans: Yes. That's a fantastic question. I can really appreciate the worry because obviously sleep is important. The good news is that I think most people think that their babies need more sleep than they're getting. The first thing that I would do is just check that professional reference that the American Academy of Sleep Medicine that shows sleep duration by age. If a baby is getting less sleep than is recommended in that chart, then I would say you probably do want to take action.

That action might be just reflecting on things that you can do at home. Maybe your child's bedtime routine isn't very stable, or you're not very good at getting your child up at the same time in the morning, or you're not paying too much attention to naps. Just trying to set a schedule, create a nice sleep environment can be a really good first step. Then if your child is still really suffering with low sleep duration, you might want to see a professional sleep expert because there may be something more complicated at play, perhaps the sleep disorder or some other medical condition that's preventing a child from getting sleep.

Emily: You mentioned naps and the importance of them. I have many memories of driving around in my car for hours on end because neither of my children were very good nappers, but they've would sleep in the car. Can you talk through what an ideal nap schedule might look like knowing that every child is different, but what should children be getting in terms of their nap schedule?

Dr. Erin Flynn-Evans: It does change over a child's life, but if we start with one of the most common trouble spots around the six-month mark, at that point, a baby should be capable of doing around a three nap schedule. Typically, the first nap happens about two hours or so after baby wakes up to start the day. That first nap would be maybe an hour to an hour and a half long.

The second nap would last for about an hour to two hours and would come two hours to three hours after the first nap. There's usually a third little cat nap that happens somewhere between two and two and a half hours after the second. I think of that just as a way to take the edge off before going to bed. You mentioned using the car and that's not too surprising because it's very difficult for babies to sleep during the day. Sleep as much lighter and only one of the two sleep drives is really promoting sleep during that daytime nap episode.

Emily: Many of our listeners are new parents and probably struggling with the lack of sleep and living on a lot of caffeine right now. What are some of the most basic things they should be aware of when it comes to getting their babies to sleep and getting them onto a sleep schedule?

Dr. Erin Flynn-Evans: The first thing is just figuring out what are appropriate and reasonable expectations. At Baby Sleep Science, we see a lot of situations where parents just don't really understand what their baby should be doing. The first step is just to say, "Okay, how much sleep does my child need? and when should my child be sleeping?" Once you figure that out, then you can further work to decode whether there's a more complicated problem at play. For example, if you have a nine-month-old baby who is sleeping from 9:00 PM to 6:00 AM, that's probably too little sleep. The first thing that I would do is work to shift, maybe that bedtime a little bit earlier to at least 8:00 PM, maybe even earlier than that.

If that child is waking frequently during the night, say four to six times overnight, that's probably reflective of that child having a sleep association, which is just an expectation that their parents do something to help them get to sleep. That could be rocking, it could be feeding, it could be dependence on a pacifier. In that case, the most important thing that a parent can do is work to teach their child how to fall asleep independently at bedtime rather than rocking to sleep, putting your child down awake, and trying to let your child fall asleep on his or her own. Then during the night, doing the same thing, maybe providing reassurance, but not doing all the work of transitioning to sleep for the baby.

Emily: I remember those nights so vividly. Unfortunately, they never really quite worked out for us. I always ended up rocking or changing their sleep arrangement from probably a lot of things that we shouldn't have been doing, but we were all sleep-deprived and needed to get the baby to sleep. What about where your child sleeps? If a child won't fall asleep in the crib, what can parents do to make their sleep environment and sleeping space a good one so that they do learn to sleep on their own in their cribs?

Dr. Erin Flynn-Evans: The most important thing is just to make sure that sleep environment is safe. The American Academy of Pediatrics recommends a flat mattress and no objects in the crib. Obviously, that's maybe not a particularly comfortable sleep environment, but it's a safe sleep environment. Once you have that sleep environment set for safety, the next things that you can do are introduce white noise.

If you live in a city and there are cars going by all night, or maybe people walking by your child's window, having white noise will help mask any of the sounds or banging pipes that might otherwise wake your child up at night, having a nice dark sleep environment. Ensuring that you have blackout shades so that in the summertime, your child isn't up at the crack of dawn. Making sure that the sleep environment is cool and comfortable. We usually recommend between about 68 degrees and 72 degrees, and obviously having your child dressed so that she's not overheated or too cold.

Emily: One thing that's been happening throughout the pandemic to kids and adults are shifting sleep schedules. No one seems to be on a consistent schedule these days. How can we help kids to avoid what you call the social jet lag of new school or daycare schedules? What can we do to make sure our kids are adjusting in a healthy way to their new sleep schedules?

Dr. Erin Flynn-Evans: That's a great question and it's a big challenge. The most important thing that you can do as a parent is really try to keep that nighttime schedule consistent within about a half-hour every day, on weekdays and on weekends. I know that that's a big ask because, the last thing that you want to do as a parent is wake your child up, especially if sleep is a trouble spot. On the weekend, if your child normally has to get up at 6:00 to go to a daycare situation, it feels pretty good if your baby's sleeping in until 7:00.

I would recommend trying to maintain that regular schedule, because what will happen is, over the course of the weekend and sleeping in, that social Jet lag that we refer to is the circadian rhythm, just shifting a little bit late. What will happen is, by the time you get to Monday, it'll be really hard to put your child down at the appropriate and regular bedtime that you had established during the week prior. It'll also be hard for your child to get up and be ready to start the day. Maintaining that regularity is really important. You don't have to be super strict, you can have about a half-hour wiggle room but that's about all you want to give.

Emily: With the seasonal time change coming up, we're about to fall back when Daylight Savings Time ends and I always hate this time of year because my daughter who is a 5 AM on the dot waker upper tends to get up at four. How do we subtly adjust this that kids can get used to the time change?

Dr. Erin Flynn-Evans: That's a great question. The time change is always a challenge for children. This used to be a time change that I really enjoyed as a child-free adult because we got an extra hour of sleep but as you point out, for children, it means that they're going to be up an hour earlier. While this is a time change, where we just shift the clocks back, it really is very similar to a one-hour Jet lag. It's as if you moved one timezone to the east. The way to solve that is to create a situation in your house that's conducive to adapting to that Jet lag. This is a little bit tricky, but I'll try to be as simple as I can.

The circadian rhythm, which is your internal body clock is one of the two sleep drives. The circadian rhythm is not particularly intuitive, it does set the timing of your sleep and awake but it sets that timing based on when your body receives morning light exposure in particular. While light in the morning resets your clock to shift everything earlier, you can introduce a bright light exposure in the evening in order to shift everything later.

The most important thing to do for this Jet lag would be to keep things very dark in the morning. If your child's up at four in the morning, you don't want to be turning on the lights and starting the day. That doesn't mean that you have to leave your child alone in the dark. You can do whatever boring and simple activities that are possible in a dark environment but you just want to keep it as dark as you possibly can until your target wake time.

Then in the evening, you want to keep the lights up as bright as you can and shift that bedtime, incrementally later, until you reach the new target bedtime. The most important thing that parents should know here is it's not going to work all at once, the circadian rhythm is slow to shift, which is why Jet lag is called Jet lag. It takes a few days for the body to catch up to a change in timing. After having bright light in the evening and darkness in the morning for three or four days, your child should adjust.

Emily: As a sleep scientist, what are your thoughts of daylight savings?

Dr. Erin Flynn-Evans: That's also a great question. I am a member of the American Academy of Sleep Medicine Public Safety Committee and we recently published a statement on this topic. I'm an author on that statement and we call for abolishing daylight savings time. It's really better for human sleep and circadian physiology for us not to have to deal with that change.

The fallback time change and itself isn't particularly problematic because we do gain that hour of sleep but in the spring where we lose an hour of sleep, there's a higher risk of heart attacks, a higher risk of accidents on both industrial and car accidents. There is a real consequence to having that time change in the spring. We would prefer to see that we maintain a single time all year round.

Emily: That's really interesting. Many parents are sleep-deprived regardless of how old their kids are. Can you talk about the importance of parents getting enough sleep? I feel like this often gets lost in the conversation and hoping you might have some advice on this front.

Dr. Erin Flynn-Evans: Yes, you're absolutely right. I think that, particularly, in the early months and years, parents recognize that sleep loss is part of the deal. As a child grows and develops, if that child isn't getting great sleep, and as a result, their parents aren't getting great sleep, it's probably worth taking some action either to help yourself as a parent or to help your child get more sleep so that you can get better sleep because if you aren't getting great sleep as a parent, you're not going to be at your best, you're not going to be as engaged with your child, you're not going to be as able to focus on the things that you need to do and all of the things that you're juggling during the day.

My recommendation for parents would be similar to what I would recommend for children, it's boring, but sleep hygiene, which is just the idea that you have a really good sleep environment and routine is incredibly helpful for adults too. You want to make sure that you have a regular bedtime, and that you have rituals associated with going to sleep. Maybe before you go to bed, you read for 15 minutes.

You want to make sure that you have a nice, cool, dark, quiet sleep environment, you don't want a television running in the background. We know that the light from screens is potent enough to influence your circadian rhythm and inhibit your ability to sleep. I would strongly encourage you to use a physical book as opposed to reading on a tablet or a screen before bed.

Emily: How long before bed should we be turning our screens off?

Dr. Erin Flynn-Evans: I would recommend that you have a minimum of a half-hour before bed, ideally, it would be much longer, maybe two hours but in the real world, you can't always follow the perfect recommendation. Certainly, you don't want that light from the screen anywhere within the vicinity of 30 minutes of going to bed.

Emily: Technology can also probably help in terms of tracking or helping us to get to sleep. Are there any particular apps or gadgets that you recommend people check out to try and help themselves or their children get some better sleep?

Dr. Erin Flynn-Evans: There's a lot of different sleep tech out there right now. For the most part, studies have shown that they're all pretty reliable. When it comes to sleep staging and saying whether you're in deep sleep or lighter sleep, they're not quite as good. When it comes to just telling you how much sleep you're getting, and whether or not that's sufficient, most of the commercial devices that you find on the market will be fine. That could be a wearable, that could be an app, that could be something that you sat next to your bed that monitors your sleep, all of those are going to give you pretty valuable information that you can use to then help improve your sleep as an adult.

For babies, there aren't a whole lot of wearables that I would recommend. We do, at Baby Sleep Science, have a partnership with Huckleberry Labs, which is a company that has created an app where you can track your baby's sleep, feeding, and diaper changes. It offers some machine learning recommendations for when your baby might be ready for a nap or might be ready for bedtime. If you're not sure where to start, as a parent, you can use an app like Huckleberry that can start to give you some guidance, and just, again, give you that starting point for solving sleep problems.

Emily: Are there any other resources that you would recommend for parents who need help with their child's sleep?

Dr. Erin Flynn-Evans: I'll give a plug for Baby Sleep Science. We have a lot of free webinars on our website, as well as blogs where we try to synthesize what we know from the scientific literature into just digestible practical information for parents to follow. We have information on the website about how to navigate newborn sleep, how to deal with toddler troubles, managing twins, and almost anything that you can think of, traveling across time zones with your child, not a lot of people are doing that right now. Once we get back back to real life, travel may become part of your world and it can be really hard to help your child adjust. We try to provide free resources that can help parents with these common challenges.

Emily: Before we end our conversation today, which has been extremely helpful, can you share one piece of advice that you would give to parents of newborns?

Dr. Erin Flynn-Evans: Absolutely. I think the most important advice that I can offer is that you should just start with the basics. Don't stress about what other people's children are doing. Don't stress about how much sleep or precisely when your baby needs to sleep. Again, schedules are important, but if your baby doesn't fall asleep at 2:00 PM on the dot, that's not the end of the world. Babies are resilient, they're flexible and one day's deviation isn't going to be the end of the world. Try to be as relaxed as possible when it comes to trying to manage baby sleep.

Emily: Erin, on behalf of all of the sleepless parents out there, thank you so much for joining us today. We really appreciate your guidance and advice.

Dr. Erin Flynn-Evans: Absolutely. Thank you so much for having me.

Outro: Thanks for listening to this episode of Equal Parts. See you next time.

Emily: Wait, before you go, I just want to tell you a little bit about Care@Work by Care.com. They work with some of the world's largest companies to offer family care benefits to their employees. If you're one of the lucky ones who already has care benefits at work, use them, if you don't, ask for them. It's a real lifesaver. To learn more, visit care.com/care@work. Again, that's care.com/care A-T work.