Kids are rebellious little runts, so I'd employ reverse psychology.

"Son, I absolutely forbid you to play Grand Theft Auto III. And if you even think about playing GTA: Vice City featuring Ray Liotta as Tommy Vercetti, I'll disown you."

The first thought that came to mind was how to convince them the errors of their way. Then it hit me, was it really a bad thing not for them to like my games? See, if they like my games, they'll want to play them. Do I really want a bunch of crayola crayon peanut butter and jellied greasy fingers all over my classic games? Even worse, if they're playing them, when the hell do I get to play them?

I also thought if my kids were playing games like those mentioned in the original post, I might have to try that game. I wasn't too interested until I read "space marine hookers". Most anything with hookers is usually a good time.