http://www.newscientist.com/article.ns?id=dn7229
"Young children who watch a lot of television are more likely to become bullies, a new study reveals. The authors suggest the increasingly violent nature of children�s cartoons may be to blame.
Previous studies have linked television to aggressive behaviour in older children and adolescents. But a team led by Frederick Zimmerman, an economist at the University of Washington in Seattle, US, has now traced the phenomenon to four-year-olds."