This is what's known as concern trolling, just fyi. Other people's kids aren't anyone's business but their parents.
I'm a parent. My youngest plays GTA. He doesn't get to play online because he gets upset too easily and I don't need him freaking out over griefers. He doesn't do missions so he never sees the stuff like Trevor doing Ashley on the counter. What he likes to do is use his single player characters with the maxed-out money (b/c I completed single for him and maxed out his money so he could do whatever he wants to) and he has me put on several cheats for hm so he can go around explosive punching things and escaping to the tops of buildings when the cops come. He also likes riding BMX bikes off the top of Mt. Chiliad.
Our culture is violent -- we don't see a lot of it because much of it is exported to other places to support our lifestyle, but it's unbelievably violent. Nearly every video game kids play is full of violence to others, including killing -- even Skylanders, which is my kids' other favorite game, has you killing others. It's freaking hypocritical to expose kids to our insanely violent culture and then tell them that they can't play this or that because it's too violent.
I play it with my kid so I can keep an eye on what he's doing and educate him about some of the sketchier things going on around him. He has no idea what a prostitute or a strip club are and doesn't even ask to do those activities. And if he did it would be a great opportunity to educate him about what's wrong with the objectification of women.
A friend of mine's kid pooled his money with four other kids to buy a copy of the game behind their parents' backs. So kids are being exposed to these cultural images/messages constantly whether their folks know it or not. At least in a game like this, if you supervise and play with the kid, you can use it to educate them about how not to be a freaking jackwad when they grow up.
This article on the subject of kids playing GTA was really interesting.