Previous studies have estimated that bullying affects 30-percent of U.S. school children.

Now a new study in the archives of pediatrics and adolescent medicine says there are steps parents can take to reduce the chance of their children growing up to be bullies. The researchers studied more than 1,200 four year olds.

They found when parents regularly read, played or otherwise interacted with their children, the chances of a child becoming a bully were reduced.

But the study showed the more television the four-year olds watched - even if they only watched cartoons, the more likely they were to bully other children.