A lack of sleep may raise children’s risk of obesity, according to a new study. Researchers at the University of Chicago found that every additional hour per night that a third-grader spends sleeping results in a 40 percent reduction in the chance that the child will be obese in the sixth grade. The study, which appeared in the November issue of the journal Pediatrics, found that sleeping more than nine hours and 45 minutes significantly lowered the obesity risk in third-graders. The authors say that their results give parents more reasons to be strict about bedtimes, limit their children’s caffeine intake and remove televisions from their kids’ bedrooms.