The more young children snore, breathe through their mouths, or stop breathing while asleep for a few seconds at a time, the more likely they are to develop behavioral problems, a new study shows. Previous research had suggested a link between these “sleep-disordered breathing” symptoms and such problems as hyperactivity, but the authors of the new study say theirs is by far the largest and most comprehensive of its kind. The researchers followed more than 11,000 children in an ongoing study in southwest England. The study enrolled pregnant women who were due to deliver between April 1991 and December 1992. For the latest findings, researchers asked parents to fill out questionnaires about their children’s snoring, mouth breathing, and apnea, which refers to abnormal pauses in breathing while asleep. The questionnaires were completed when the children were 6, 18, 30, 42, 57, and 69 months of age. When their children were 4 and 7 years old, the parents were asked to complete questionnaires about their children’s behavior.