When my son was around 4 I was playing GTA and was not playing it violently when I took a car from someone and they tried to pull me out he said "Hit him dad! Hit him!" but never in his life (he is 21 now) has he struck anyone. It was just a game to him.
A week ago I pulled out my warhammer miniatures and my 5 year old picked the leader and started shooting and stabbing people. Then she proudly stated that he was "collecting dead people".
I was quite surprised because her normal play involves taking care of her baby dolls.
The morbidity of children never ceases to amaze me. Death, in play at least, doesn't seem to frighten them. I guess its the same among adults, but it's interesting that make-believe and reality are seperable even at a young age. I don't think we adults give kids enough credit for how sophisticated they can be. (Probably because there are a lot of areas where they aren't and it's easier to just bucket them in whole.)
One thing I (thankfully) realized pretty early on when raising my kids is that they're fully-intelligent humans pretty much from the start. They just dont _know_ stuff, but their intelligence is all there from a much younger age than most people seems to think.