Good question. I discussed this issue at length with Sandy Newmark, M.D., a pediatrician at the Osher Center for Integrative Medicine in San Francisco. He says that the most important thing is that "children get enough sleep, and that they have a regular bedtime. It is OK if some of that sleep is from a nap." However, Dr. Newmark also says that there is no easy answer to the question of whether allowing a late-night bedtime due to napping or other reasons is OK. He notes that some experts believe the amount of sleep obtained before midnight is important and that "we do know that sleep before midnight has a different proportion of REM and non-REM sleep than sleep after midnight." Our brains are active and we dream during REM sleep, while during deep non-REM sleep the body is busy increasing the blood supply to muscles and restoring energy. During the latter state, tissue growth and repair occur and hormones are released for growth and development.
Dr. Newmark adds that "we evolved as a species to fall asleep after sundown, so it is probably better for children to have a relatively early bedtime. If your child is going to bed at nine o'clock instead of seven, I would say that is no problem. If he is going to bed at 10 or 11 p.m., I would try to make it a little earlier."
You may be interested to know that research from the U.K. published in November 2013 found that children with regular bedtimes, regardless of whether they were early or late, had fewer behavioral problems compared to kids whose bedtimes were irregular. In fact, the researchers from University College London found that the more years irregular bedtimes persisted, the more severe the kids' behavior problems were. They gathered their information by interviewing mothers when their children were ages three, five and seven. Both mothers and teachers completed questionnaires about behavioral problems. The researchers reported that almost 20 percent of three-year-olds had no regular bedtime, compared with 9.1 percent of five-year-olds and 8.2 percent of seven-year-olds.
Commenting on the findings, the study's lead author, Yvonne Kelly, a professor of epidemiology, said that "getting kids into a regular bedtime routine does appear to have important impacts on behavioral development," but she made the point that lots of things have beneficial effects and that regular bedtime is only one of them.
For the record, according to the National Sleep Foundation (NSF) parents should expect preschoolers to sleep 11 to 13 hours per night and not expect most to nap after five years of age. The NSF notes that difficulty falling asleep and waking during the night are common in this age range and that with normal development of imagination, preschoolers commonly experience nighttime fears and nightmares. Sleepwalking and sleep terrors also peak during preschool years.
Kids aged five to 12 need 10 to 11 hours of sleep a night, but in this age range they also are dealing with increased demands on their time from homework, sports and other extracurricular activities, as well as television and computers, all of which can cause difficulty falling asleep, nightmares and sleep disruptions. The NSF warns that watching television close to bedtime has been associated with bedtime resistance, difficulty falling asleep, anxiety around sleep and sleeping fewer hours. What's more, the Foundation notes that poor or inadequate sleep in kids this age can lead to mood swings, behavioral problems such as hyperactivity, and cognitive problems that impact on their ability to learn in school.
Andrew Weil, M.D.
Yvonne Kelly et al, "Changes in Bedtime Schedules and Behavioral Difficulties in 7 Year Old Children," Pediatrics, (doi: 10.1542/peds.2013-1906)