(the following comes from my stock of old posts I kept from the yahoo group I used to run...)
One thing that needs to be addressed is the issue of media violence. I think normal good guy bad guy stuff is a vital part of childhood - but I also think that one has to put it into context. Just as we wouldn't want our children doing good guy bad guy stuff role playing Cowboys and Indians in this rather more enlightened day, I think one does have to help children find healthy outlets for this kind of play. Nourishing stories such as fairy tales and legends from many cultures give a good set of roles for a child to work with.
However, though it might be fairly straightforward for us to ensure that our own children get the kinds of images and archetypes we feel is healthy for them, we can't guarantee that that is the case for the children they play with. That's when it gets tough. If other children are playing Grand Auto Theft as you say and bringing that to your children than I think it's decision time - are these children you want your child to play with? It may be possible to ask their Moms to not let them "play" (and many people unfortunately think that video and game boys use is play) with those things when your child visits but that's not going to stop the talk and excitement about it if that's the hot game at the moment. Then I think the only recourse you have is to firmly let your child know that you don't approve of these things, that unfortunately, so-and-so has this game but that you feel it's not for your family.
But I also think that this is delicate - you don't want your own child to feel bad about being interested in these things - and from your post(that I am responding to) it seems he is conflicted. Of course he is. And he needs to be able to work this out. I would suggest that you make your feelings clear to him - but that you also make sure you say plenty of positive things about these other boys. I think you should completely ignore the comment about "killing" you - he no more means that then a furious 4 year old means it when she screams "I hate you". He is simply experimenting with something that is obviously important - look how upset his mother got!
A primary way of approaching things like this from a Waldorf perspective is to always, when possible, redeem. Redeem, metamorphose, transform. Find the good, turn things around. It can take effort - if your son is a leader in the group, then give him roles and skills to bring to his friends. Find some heroic stories like Hiawatha the Peacemaker in my Saints & Heroes book or of Lancelot or Robin Hood - maybe he can bring some of that play to his friends. And if he can't because he's embarrassed or too young then don't worry - even if they seem to playing the most disgusting games you don't know what's going on in their heads, what their own internal dialogue is during this play. He might well be redeeming such things himself. And if you give plenty of story material that shows how this can be done - just as a matter of course, not telling him that this is what you're doing - and if you don't make him feel bad but make him feel supported in his search for what is good and true, then he'll come through just fine. As a youth worker with 20+ years experience working with all kinds of children - most from very rough non Waldorf backgrounds who didn't just have violence on their tv's but in their own lives - I can tell you that it can be ok. Trust your son, trust your powerful ability to love and see your role as redeemer. Consciously take in those media images - and in your prayer or meditation, transform them.