"Among the many fantasy roles that children take on their play are good guys and bad guys. Once known as cops and robbers, this kind of play is now more likedly to involve superheroes or fantasy characters from TV and movies. The main thing for parents to remember about this type of play is that it isn't as destructive or as horrid as it may seem. Well, superhero or good guy/bad guy play is a human way of practicing control over aggression. Some children prefer to be the bad guy, experimenting with being frightening or dangerous. Actually hurting people isn't helpful, but playing at it can be both fun and educational -- in the sense of learning to manage aggressive feelings and impulses. Other children prefer to be the good guy. They like to be aggressive in a way that is socially accpetable -- by being Batman, for example, or a soldier. THat is, they get to exercise their aggression but only at acceptable targets.
Some parents love this kind of superhero play and get into the characters along with their children. They understand that if they are playing the role of the bad guy or the monster, they need to be not too scary -- powerful enough to be interesting, but not overwhelming. Maybe a little bumbling or incompetent (like Lex Luthor in the Supermann movies). Other parents hate this kind of play and would love to ban it. Sorry. Children who want to play these games need to play them, and if they aren't allowed to, they will go underground and do them anyway. It is much better to join and play with them, which then lets you shift the play a little bit if it gets too violent or out of hand."