I've also been referred to as male, asked which gender I was, etc. by kids while presenting as female. I, honestly, don't seem to pass as female all the time, even though I have long hair and an obviously female body. That's one thing I don't have to worry about in regard to transitioning (though I do have plenty of other fears about it).
Anyway, I think it's cool that kids seem to pick up on people's true gender identities better than adults do. It's like they go by the person's attitude, not the shape of their body. And I like it that they're so directly honest about things.