Yes, there are a lot of games which show killings in graphic details. And all it takes is a just few clicks for your child to get hooked on to them. But it's not really 'the element of violence' that a child is getting hooked on here-it's the sense of having power and being in control.
Games are violent because that's what the kids prefer.
Very few kids prefer educational games. So it stands to reason that the more violent the game is, the better it will sell. Kids are no longer interested in simple animation, and educational games. Some experts believe that violent games are a means of interaction between children. It can be a release of violence and aggression which they may have within them.