I remember my parents having this discussion.
My mother would happily have forbidden us to play "cowboys and indians" and have cowboy hats, guns gun-holsters, feather headresses and tomahawks.
My father said that she could forbid it as much as she liked, but that we would continue to play, using our fingers or sticks instead of a toy gun or tomahawk. He explained to us that it was all right to play games like these because they were only pretend, but that in real life if you shot someone that person might very well die.
He forbade bows and arrows, slingshots and catapults, because with any of these you could kill someone.
A child of five has got to the stage of trying to assimilate what death actually is. Playing cops and robbers, hospitals, Robin Hood and so on is part of this process.
This doesn't mean that I think children should be allowed to take toy pistols out shopping with them and run around "shooting people", but playing at home with these toys, can and should be a way of tackling the difficult subjects of death, injury, war and terrorism. We can't protect children entirely from hearing about all this, after all, so we need to find a way of answering their questions about them.