I'm with Dragonfly ("Let it happen.")
I think it's pretty normal for boys. MOST boys seem to want to do it (that's why I think it's normal.)
Here is an e-mail I sent to friends recently: DS has been driving me up the wall lately with his aggression. Just being very physical with me and DD. Not in a "bad" way like he's angry with us or acting out frustration, more like he can't help himself. I'm so frustrated because all the talking and explaining is not working. Which leads me to "punishing" which I'd rather avoid, but I don't see any alternatives right now. Even my friend was saying that (sweet little) Eric will walk past his older sister and just hit her for no reason, causing his teenage sister to yell "I've had it! Cut it out!!"
Then yesterday in the toddler class (mommy & me at my local developmental parent co-op preschool), Ms. Frost talked about Cognitive Development, and handed us some excerpts from
THE WONDER OF BOYS by Michael Gurian. Reading this helped. She suggested giving him outlets (outside play, playdates with friends, etc...):
- Boys have more testosterone in them, which makes them naturally
more aggressive and physical. Risk taking is programmed into boys.
(I noticed that. That is why I never discouraged DS from jumping from the tallest spot on the jungle gym in the park. I figured if he felt he could handle it, then he could do it.) It's important to distinguish between aggression and violence.
Aggression is hard-wired, violence is taught.
- On the average, a little boy will turn toys into guns or swords.
(I met a crunchy mom once who was did not allow guns. She said her boys
turned TOAST into guns - LOL.) He'll hit more, he'll be competitive. More need to dominate and less empathetic. Depending on his personality, will seek rough and tumble play or another outlet for aggression.
- Little boys are more right brained dominant, meaning more interested in spatial relationships (which explains why he is driving us nuts with insisting on playing with BALLS in the

house.

Tossing them up in the air, across the room, etc... ) and activities instead of social relationships and communication. They like to throw things and climb..... they need space!
- Generally speaking, girls read emotions more and are more intuitive, causing them to be more verbal, group oriented and social.
- In the beginning, boys have more reading difficulties but are better in math. This is due to right brain dominance.
- Girls cry more than boys because they are more in tune with emotions. Boys react to stress with action and problem solving.
I don't buy guns either. Not any gun that looks like an obvious black uzi (like General Grievous'

: gun.) But I do allow "space blasters" that look and sound like space blasters (cool sounds) - that is our compromise.
He has a pile of swords (including light sabers). That's fine by me.

When DS was 4, he wasn't into guns or swords much. He was into princess dresses.

He just about lost it when he first saw a wall of pretty GLITTERY dresses in the Disney store. At first I tried to deter it. Then I just embraced it. DH

was annoyed

: and worried about it. Within a year, he got over it. My only rule was he wasn't allowed to go to our local park ("why???") wearing it, and we all know why. Same thing with guns. He can't take them to the local park to start shooting friends. Sorry.
Anyway, my point is, it's just play. Let them play and explore. Cohen's book should help.

It doesn't mean my son will grow up to be a cross-dresser or a pirate or a criminal.