Well, You can't blame entirely a videogame.
IMO Videogames are just like TV, Computers, and stuff, is a medium, a tool taht can have good and bad things depending on what you look for on them. So a kid playing a game not suitable for his age is a bad as seeing this same violent movie or getting into bad sites on internet, of course what he see will affect his or her behavior, as this kind of stuff marks a deep impact on them.
Must of them got labels, wheter is a site a movie or a videogame, they all have ratings. Of course taht doesn't take out the risk of kids lying their hands on such stuff, but i think here the fault doesn't go taht much on taht stuff as it goes into the careless people around the kid.
I'll post more later, is kind of late right now.