Young kids playing violent adult-rated games all day while unattended? Yeah, I guess that's a bad idea but it still ultimately comes down to bad parenting and nothing but. I mean, me and my brother shot nerf guns at each other for over 10 years, saw R rated movies like Die Hard before we were even 10, played some somewhat violent games like Goldeneye, and all that but I'd like to say we came out fine and won't be killing people at random any time soon. In fact I think being exposed to all that only helped me mature a little sooner. I also had good parents and I respected them and what they said, for the most part. This sick fuck killed his mother in the process which leads me to definitely think it was a family feud and he decided to take it out on a bunch of kids that had nothing to do with it in the process.
If anything, I think violent videogames can be good. I'd like to say the vast majority of gamers and aware that games aren't the real world and it can be a nice stress reliever when you get to shoot your buddies in the face a bunch of times without anyone actually getting hurt in the process. Case in point, I really don't believe this could possibly have any basis for being true.