I just thought I'd present an argument about video games and violence. I suppose there are some studies that show that violent video games increase aggression, but I believe that there are cathartic effects to playing games as well. After all why really kill people when you can commit as much violence as you'd like with no danger to yourself in fantasy? Looking back to times before we had much violent media, we see the most violent wars in American and European history. There occured both world wars, the American Civil war, before that tons of medieval fighting, before that Roman Conquest and gladiator matches, etc. Nowadays we still have war, but also an extreme distaste for it. With war simulation games resulting often in player death, I think it seems logical that people would attempt to avoid that happening in reality. On a domestic level, I've seen graphs that suggest a decrease in violent crime with the increase in violent video games, supposedly based on federal reports, but I question their validity.
Perhaps violent media played no part in this, and we should attribute everything to economic developement. However, taking this argument also limits how much one could attribute violent games with adverse effects as well.
I don't mean to argue for allowing children to play violent games at a young age, as I think this could lead to philosophically pessimisstic views on reality. However, less violent video games offer a lot of things, like patience, helping others, problem solving and observation, reading and vocabulary, etc. As long as you keep your kid from devoting all their energy to games and not other, healthy activities like exercise, art, etc. I doubt you'll run into many problems. However, from personal experience I'd like to say that limiting game time, etc. is only so effective. My parents limited the time I spent with games, signed me up for sports, activites, etc. which I participated in completely and I still ended up less a social person than they hoped I think. They also paid diligent attention to movie and video game ratings until I was a teenager, and I've ended up with a full ride to a good school, all A's, good friends, and only occassionally have a few drinks (but hey, that's legal in the parts of Canada where I'm from).
Hope this helps, and I hope it wasn't too long.