Okay, yeah a kid can be affected by videogames as much as any other media. Kids aren't total morons, but they can still be affected by certain things they see and they may attempt to emulate it. Some kids may simply go "cool" others may begin to live and breath it. There is however one thing that can help prevent it: Don't let them play it. Most kids can't even afford a 20 dollar game, let along a 60 dollar one. Don't buy your kids a game called GRAND THEFT AUTO. Though, there are other factors that can end up getting the game into a child's view, let alone hands.
Older relatives who can actually afford this game may play it in front of someone kids. Whether it be an older brother, cousin, or hell even the father. Parents can ask them to not play certain games in front of them, but sometimes they won't really care. Let's be honest, no remotely intelligent parent would ever buy an actual "child" a truly violent videogame. However, if they do...well, good on ya. You should know what you're exposing your child to and have to ask yourself if they can take it. If you can't answer that...don't fucking buy them a violent videogame!
I can see why a lot of kids are turning predominantly to violent videogames though. Aside from popularity, there's not really a lot of interesting E games coming out for major consoles. Aside from the blatant Mario, Zelda, Kirby, Metroid, and other Nintendo titles there aren't a lot of compelling multi-platform E rated games. All I see are sports games, movie games, quiz games, tons of shovelware and that's pretty much it aside from a few sidescrollers, downloadable games, and a few random exclusives.