Television viewing is being linked to sleeping trouble in preschoolers.
Seattle researchers found that sleep problems are more common in three to 5-year-olds that watch TV after 7 p.m.
Roughly 21 percent of the study group were found to have difficulty falling asleep, experienced nightmares, and were tired during the day.
"We definitely thought there would be an effect from violent content and evening content, but we saw that any evening content was a problem -- it didn't really matter for sleep if it was violent," said study author Michelle M. Garrison, a research scientist at Seattle Children's Research Institute.
Garrison also noted that even violent cartoons caused sleeping problems in small children.
"Older kids can grasp what's real and what's not. To preschoolers, animated violence is just as scary as real violence," Garrison explained.
The study showed that non-violent programming viewed during the day did not seem to have much of an effect on toddlers' sleep.
The survey, based on reviews of parent surveys and media diaries from 617 preschoolers, will be published online June 27 and in the July print edition of the journal Pediatrics.