Haha. If you think about it, Mario would be considered violent. Jumping on turtles and kicking them is pretty violent behavior
But seriously, I watched R-rated movies when I was like 9 years old. My parents did limit the types of R-rated movies that I could watch and they made sure that I understood that real violence is never good.
Basically what I meant to say is that many parents don't supervise or talk to their kids about violence in movies, TV, or videogames. They let their kids play violent games all day every day and don't instill in them that violence is wrong and that these games and shows are not real life but fake. If parents don't do this then their kids begin to think that maybe this is what real life is like(outside of their comfy home and school) and that it is OK to do the things they see in violent movies or games.