Chicago ? If your preschooler can’t sleep — turn off the violence and nighttime TV.

That’s the message in a new study that found sleep problems are more common in 3- to 5-year-olds who watch television after 7 p.m. Watching shows with violence — including kids’ cartoons — also was tied to sleeping difficulties.

Watching nonviolent shows during the day didn’t seem to have any connection with sleep problems in the 617 youngsters studied.

The study builds on previous research linking media use with kids’ sleep problems, and also bolsters arguments for limiting children’s screen time.

The American Academy of Pediatrics recommends no screen time for children up to age 2, and no more than 2 hours daily for older children. It also urges pediatricians to ask parents at every checkup how much their children watch television, including whether kids have TVs in their bedrooms, which the academy discourages.

Previous studies have found that at least one in four U.S. preschoolers have TVs in their bedrooms, and many families mistakenly believe that watching TV will help their kids sleep, said Dr. Michelle Garrison, lead author and a scientist at Seattle Children’s Hospital Research Institute.

The government-funded study was released online today by the journal Pediatrics.

Overall, about 112 kids studied — nearly one in five — had one or more frequent sleep problems most days of the week. These included difficulty falling asleep, awakening repeatedly at night, nightmares or daytime sleepiness.

Kids who watched the most nighttime or violent TV had the most sleep trouble. TV was the main source of screen time rather than computers or video games.

The study relied on parents’ reports of kids’ sleep difficulties and TV habits, and wasn’t rigorous enough to tell whether TV caused sleep problems. It could be that poor sleepers might be more likely to watch TV; or family factors such as lax parenting could have been involved.