any of my friends criticize that fact a lot, but I think it's good that violence is more acceptable than sex as viewing for kids. Why? Simple. Almost every single 5-year-old has been in a pushing match, a fight over toys, or something similar. Violence is something that cannot be avoided; there's some degree of violence in pretty much everything, and kids get used to it.
Kids can understand violence, and most of them can understand that there's a difference between punching Tommy in the nose to take your blocks back and stabbing Tommy just for being there. Exposing kids to some level of violent content helps them understand that violence is a fact of life, and helps them understand what levels of violence are acceptable or unacceptable in which contexts.
However, sex is difference. The hell with what Freud said, young children do not have sex drives. Period. They just don't, until they're around 12 years old - 9 years old in rare cases. Young children can't intuitively understand sex; they can't go experimenting with sex with their friends like they can with violence. It would have extremely bad consequences on their mental development, they'd likely be mocked and/ or ostracized, adults would freak out, and given their state of physical development most of them wouldn't, er, learn anything anyway.
In summary: Exposing kids to violent media is unlikely going to screw up how they view the world because their friends will expose them to normal levels of violence. Exposing kids to sexualized media is likely to screw up how they view the world because they can't learn how sexuality is in the real world at that age, and the damage will be done by the time they can learn.