A three year old is going to hurt himself for not being allowed to participate? You're actually being serious? Keep this in mind the next time you're watching kids get pulled out of the Audience to dance at lion king. Then pay attention to the other toddlers who are committing mass suicide.
I'm not even going to get into the "gender conforming" comment- we simply won't ever agree on that front.
As for your future child's happiness, you simply say "sorry Noah, it's just for Girls." Then, your future kid will ask for goldfish, give them to him. He's now happy. Or- you can make a blog and be devastated. Again