I'm pretty sure the way parents and other treat children has a huge effect on how they in turn treat others. If children encounter double standards and unfair treatment, they will learn it. They also understand very well that a game world is a game world, and you are supposed to play the game. But if in the game world they are teased or treated unfairly, it will have a negative effect on their personality - just like in the real world.

So I don't think violent games should be banned, but bad behavior towards children.