Once a kid is in their mid teens, there really isn't much you can do to stop them from playing GTA, downloading porn, listening to gangsta rap, ect. Even the "good kids" do this. If they were raised right, such influences won't lead them astray.
pretty much...
the teenage years are when kids run into things that hopefully their parents have prepared them for....
parents can't prepare kids for everything, but they can give the kids the foundation needed. My parents did and it wasnt that hard....