Truth be told, I think a lot of people overestimate the effects "mature" games have on kids. Or maybe rather underestimate childrens ability to tell the difference between games and real life.
My own example being that I've had some sort of gaming medium, or several, at my disposal for as much time as I ever wanted, since I was 5.
Of course, this was back in the late 80's- early 90's so games weren't as photo-realistic, but on the other hand there wasn't any sort of parental guidance rating either.
Whatever came on those goldmines of cracked game compilations that my father bought back then I was welcome to play, as long and intensely as I wanted to.
Of course, working in gaming retail today its always a hoot when you tell parents "Yeah GTA, its mostly about stabbing hookers, ramming old people with your car and shooting cops". The look on their faces, its priceless.
In the end, I don't think there's anything wrong with games, its people thats the problem