The new findings don't surprise Dr. William Muinos, director of the weight management program at Miami Children's Hospital in Florida, who was not involved in the study.
His advice for parents? Set a consistent bedtime. "Limit caffeinated beverages late in the day. Cut out all those electronic distractions; get them out of the bedroom," Taveras said.
Insist that children go to bed earlier, Muinos said. "Lack of sleep does change the physiology," he added. "It will put you in what is called stress mode. The body will read it as, 'I need to hold onto calories and accumulate fat.'"
The new research, Muinos said, "is very good because it studied a large group of children for a long period of time."
Ongoing studies are looking at whether improving sleep may directly improve weight control in children, Taveras said. And it's already known that good sleep has other benefits. "There's really good evidence that shows it improves schoolwork," she said.
For the study, mothers reported their children's usual sleep duration in a 24-hour period, beginning at age 6 months. They also reported it every year from age 1 to 7.
The children got a sleep score, ranging from zero (insufficient sleep) to 13 (consistent sufficient sleep). The average sleep score was 10.2. However, about 4 percent of kids were in the insufficient range, zero to 4. About 40 percent had a score of 12 or 13, termed enough sleep.
Those who slept less than average were more likely to be from poorer families with less educated mothers, the study found.