The quantity and the content of television viewing by children may effect social behaviors long term, with effects that may last into adulthood.
One study followed 1,037 people from birth to age 26 years and found a significantly increased risk for antisocial outcomes in adults who had watched the most TV as children.
In another study involving 565 pre-school aged children in the United States, coaching parents to reduce viewing of violence on the screen and to increase exposure to prosocial programming resulted in significantly less aggression and more prosocial behavior in the children.
TV's didn't become commonplace in American homes until the 1950's.
I don't think it's a great leap to suspect years from now a similar study will be released in regards to the graphic video games many of our children spend hours a day playing.
When our children were young, my wife used an old fashioned kitchen timer and allowed our kids only one hour a day of "electronic time (TV, video games, etc)."
My daughter never had a problem with it.
My son hated the timer but complied.
They both knew that when the alarm sounded electronic time was over for the day.
It was time to get outside and play.
More parents need to do the same.