Children may know that guns are dangerous. They may even know that guns kill. But they don't understand the power they wield to eliminate life- permanently. Kids can make any object, from their finger to an empty paper towel roll to a real gun- be a gun. But to children, playing with guns, pretend or otherwise is a game.
Nobody really dies.
Your best friend still comes back to play with you the next day, even after you killed him. At least that's the way it works in a child's world. However, improper use or abuse, can be fatal, especially to a child. Before child-proof lids became standard on medicine bottles, children died from an overdose of too accessible medicine. The children didn't understand the medicine was dangerous, after all, they were just playing.