In the classic "Bobo doll" studies, children witnessed adults play with a rubber, inflated toy. The adults either behaved aggressively towards the doll, such as hitting it with a hammer, or kicking it, or interacted peacefully with the doll.
Albert Bandura (currently at Standord University), the lead scientist behind these studies, thought that the children would play with the doll in whatever manner they had seen the adults play with the doll. This is precisely what the studies found.
The practical message is clear: Children learn their behaviors from adults. If we are to have a more peaceful world, it starts with the way adults act around children.
The crux of Bandura's social learning theory is that children (and adults new to situations) learn from others in the environment how to behave. The key to this, in terms of aggression, is not merely telling the children not to be aggressive or explaining to them why they should be peaceful, but rather, to have them witness adults behaving peacefully. Children will mimic the behavior, and in turn, become more peaceful themselves. That is, they will model their behavior after the adults they have seen behave a certain way.
Bandura's social learning theory also seems to have implications for how children react to viewing aggressive and violent television, movies and even video games. Studies show that children and teens, on average, become more aggressive after playing these games and viewing these shows. From Bandura's perspective, perhaps these children and teens are "learning" such aggression through the actions of the people on the screen.
This is not to say that every child who is aggressive/violent learned it from watching the behavior of his or her parents, or from television. It also is true that genetics and biology (like testoterone levels) play a role in determining aggression.
However, on average, if parents are aggressive they are more likely to have aggressive children if they show that aggression to their children. And, on average, viewing aggressive movies and shows and playing violent games increases aggression.
To see video examples of Bandura's study: