A new study by Ohio State University shows preschool-aged children who go to bed late have a higher risk of obesity as teenagers.
Lead researcher Doctor Sarah Anderson says that also leads to problems in school.
The study, funded by the National Institutes of Health, followed more than a thousand children for more than a decade. It found that nearly one out of four pre-schoolers who went to bed at nine o'clock or later became obese as teenagers. Anderson says pre-schoolers need ten to 12 hours of sleep a night. The study is published in the "Journal of Pediatrics."