Tough and controversial subject. It used to be "cowboy and indians" make believe...standard stuff. These days, it may as well be about acting out "gangsta" fantasies. Different times, different strokes...
Toy guns, video games, toy soldiers...whatever. Its about acting out chilidish fantasies and scenarios without (hopefully) any propensity or desire for true, adult like violence. Plus, there is the factor of simple, positive aggression release and oh yeah... having fun! Many will purport that games and plastic guns encourage youth violence, but I say this is essentially crap as this stuff has been around for many, many years.
"Playtime" for children and the means thereof have not really changed much as far as Im concerned. Rather, such things (in todays world) have unfortunately, for many reasons, taken on a whole new, perverted meaning. Its just a stupid shame (thanks in part to shameless, irresponsible media coverage..but I wont go into that).
Outside of living in a bubble, proper parenting, guidance and/or mentoring usually goes a very long way. Even then, some will go astray. But, many wont. Its always been this way to one degree or another and it will never change.