Hey,
I am one of seven children in my family and most of them are under 12. My younger brothers have gotten into playing cpu games like half life and the origional doom and i think that it affects them heaps. one of the younger ones who is 5 has gotten into saying things like "I stab you face with a dagger" and "I will cut your eyes in open!" and so on.
This may not be exclusivly from violent games but scince they are too young to understand that it is all fake they take it too seriously.

For older people like teenagers and up violence isn't as much of an issue. But now games are getting into Drugs, Language and Sex (Like GTA) and this is making them even worse (Not to say that games like GTA arnet fun .)

I don't think that games should be made with small amounts of violence and everybody hugging or holding hands BUT they should have options to turn off unsutible content so that when smaller children play them they dont annoy the crap out of you afterwards because they have picked up somthing from them.

But that is just my opinion.