A little, and only as an association. In a Frontiers in Public Health study of 49,208 Japanese toddlers, published 24 September 2026, those who fell asleep before 10 PM at 18 months grew about 0.13 cm more by age 3 than those asleep at 10 PM or later. The authors call the difference small and not proof of cause.
Key takeaways
- A nationwide Japanese birth cohort study of 49,208 toddlers, published 24 September 2026 in Frontiers in Public Health, linked falling asleep before 10 PM at 18 months with slightly more height gain by age 3.
- The gap was about 0.13 cm over 18 months, which the authors describe as small; the study is observational and cannot show that bedtime causes growth.
- About 1 in 5 toddlers in the study (18.8%) fell asleep at 10 PM or later.
- The American Academy of Sleep Medicine recommends 11 to 14 hours of sleep per 24 hours, naps included, for children 1 to 2 years old.
- The one change: set a consistent bedtime routine that ends with lights out well before 10 PM, and keep it the same every night.
What did the 2026 toddler bedtime study find?
Toddlers who went to sleep earlier grew a little more over the next year and a half. Researchers at Tottori University analyzed 49,208 full-term toddlers from the Japan Environment and Children’s Study, a nationwide birth cohort.
At 18 months, caregivers filled in a 24-hour sleep chart, marking whether the child was asleep or awake in each 30-minute slot. Bedtime was grouped as early (8 PM to 9:59 PM, plus any child asleep before 8 PM) or late (10 PM or later). Height was then followed at 2, 2.5 and 3 years.
| Finding (18 months to 3 years) | Result |
|---|---|
| Toddlers in the early-bedtime group | 81.2% (39,968 children) |
| Toddlers asleep at 10 PM or later | 18.8% (9,240 children) |
| Extra height gain, early vs late bedtime | about 0.13 cm over 18 months |
| Night sleep of 10 hours or more vs less | no clear difference in the main model |
| Waking 3 or more times a night | no clear difference |
The models adjusted for sex, parents’ heights and education, and household income.
Does an earlier bedtime make toddlers taller?
The study can’t say that, and the authors say so plainly. Earlier bedtime was associated with greater height gain, but the design is observational, so families with earlier bedtimes may differ in other ways, such as nutrition, daytime activity, screen exposure or health, that the data didn’t fully capture.
The gap is also small: about 0.13 cm over 18 months. The authors note other limits:
- Sleep was reported by caregivers on a single questionnaire at 18 months, with no wrist trackers or other objective measures.
- Many children were excluded for missing measurement dates, which could bias the sample.
- Bedtime habits may have changed after 18 months.
The authors suggest one possible reason for the link: growth hormone release is tied to sleep onset and deep sleep, so an earlier sleep onset may line up better with the night’s main growth hormone pulse. They did not measure growth hormone, so this remains a hypothesis. Their practical point is modest: bedtime is easy to raise at routine child health visits.
How much sleep does a toddler need?
The American Academy of Sleep Medicine recommends that children 1 to 2 years old sleep 11 to 14 hours per 24 hours, naps included, on a regular basis. Children 3 to 5 years old need 10 to 13 hours. A bedtime before 10 PM makes those totals easier to reach when mornings start early.
Why does a bedtime routine help?
A consistent bedtime routine has trial evidence behind it for young children’s sleep. In a 2009 randomized trial published in Sleep, 405 mothers of children aged 7 to 36 months were assigned either to keep their usual evenings or to follow a nightly three-step routine (a bath, a massage and quiet activities like cuddling or a lullaby), with lights out within 30 minutes of the bath. After two weeks, children in the routine group fell asleep faster and woke less often and for shorter periods during the night, and mothers’ mood improved. The trial was funded by Johnson & Johnson, which supplied the bath and massage products, and lasted only three weeks.
A 2015 study in Sleep, based on questionnaires from mothers of 10,085 children up to age 5 in 13 countries, linked a consistent bedtime routine with earlier bedtimes, falling asleep faster, fewer night wakings and longer sleep. The more nights a week families kept the routine, the better the sleep outcomes were.
What is the one change to make?
Build a short, repeatable bedtime routine that ends with lights out well before 10 PM, and run it the same way every night. The 2026 study doesn’t prove that bedtime drives growth, but an earlier, consistent bedtime fits the evidence above and costs nothing.
- Count back from wake time. If a toddler wakes at 6:30 AM, a 7:45 PM lights out leaves room for close to 11 hours at night, with a daytime nap on top.
- Start the routine 30 minutes before lights out: bath, pajamas, a book, a cuddle or song.
- Keep the order the same every night, including weekends.
- Dim the lights during the routine and keep the bedroom dark and quiet.
- Move the time in small steps. If bedtime is late now, shift it about 15 minutes earlier every few nights.
For the adult side of the evening, see How to Fix Your Sleep Schedule: Anchor, Light, 15 Min and Best Time to Eat Dinner? What the Evidence Says. Sleep timing keeps mattering as kids grow: Do Later School Start Times Help Teens Sleep More? looks at the teenage years. Curious whether you run early or late yourself? Take the Body Clock Type quiz.
Your day on My BodyClock
The day above on My BodyClock shows a working parent’s day built around an early, steady toddler bedtime. The parent sleeps from 10:30 PM to 6:30 AM and fits focused work between daycare drop-off and pickup.
After pickup come a walk to the park, family dinner at 6 PM and quiet play. At 7:15 PM the bedtime routine begins: bath, pajamas, a book and lights out by 7:45 PM. A Flow block resets the kitchen, then time with a partner and a lamp-lit wind-down lead to the parent’s own sleep.
Swap in your family’s wake time and count back. Build your version in Owaves: My BodyClock on the App Store, or join the Android waitlist.
FAQ
What time should a toddler go to bed?
Most toddlers do well with a bedtime that lets them reach 11 to 14 hours of sleep per 24 hours, naps included, as the American Academy of Sleep Medicine recommends for ages 1 to 2. For a child who wakes around 6:30 AM, that usually means lights out between about 7 PM and 8 PM.
Does sleep affect how tall a child grows?
The evidence links sleep timing with growth, but only weakly so far. In a 2026 study of 49,208 toddlers, falling asleep before 10 PM at 18 months was associated with about 0.13 cm more height gain by age 3. The study was observational and the authors say it does not show cause.
Is 10 PM too late for a toddler to go to sleep?
In the 2026 Japanese study, 10 PM or later counted as a late bedtime, and about 1 in 5 toddlers fell into that group. A late bedtime makes it harder to reach the recommended 11 to 14 hours of sleep when mornings start early. If bedtime runs late, move it earlier by about 15 minutes every few nights.
Sources
- Senoo S, Shimizu K, Fujimoto M, et al.; Japan Environment and Children’s Study Group. Earlier bedtime at 1.5 years is associated with greater height gain at 3 years of age: a nationwide birth cohort study of the Japan environment and children’s study. Frontiers in Public Health, 24 September 2026. doi:10.3389/fpubh.2026.1945746. https://pubmed.ncbi.nlm.nih.gov/42851434/ (full text: https://pmc.ncbi.nlm.nih.gov/articles/PMC13646113/)
- Paruthi S, Brooks LJ, D’Ambrosio C, et al. Recommended Amount of Sleep for Pediatric Populations: A Consensus Statement of the American Academy of Sleep Medicine. Journal of Clinical Sleep Medicine, 15 June 2016. doi:10.5664/jcsm.5866. https://pmc.ncbi.nlm.nih.gov/articles/PMC4877308/
- Mindell JA, Telofski LS, Wiegand B, Kurtz ES. A nightly bedtime routine: impact on sleep in young children and maternal mood. Sleep, May 2009. doi:10.1093/sleep/32.5.599. https://pmc.ncbi.nlm.nih.gov/articles/PMC2675894/
- Mindell JA, Li AM, Sadeh A, Kwon R, Goh DY. Bedtime routines for young children: a dose-dependent association with sleep outcomes. Sleep, 1 May 2015. doi:10.5665/sleep.4662. https://pubmed.ncbi.nlm.nih.gov/25325483/
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