[Nora Wex]

Sometimes people need to learn on their own what life's about. He's going to have his own friends and his own experiences to teach him a lot of things by himself. A lot can change in a year, so he'll likely grow out of a lot of things. If you don't tell him, maybe someone nicer will. You need to have a sit down talk with your mom and make sure you don't raise your voices. Communicate calmly and stake your case.

Tell her something like this:

"Mom, I'm worried about my brother because he's a little too old to be believing these things anymore. I know you want him to stay young and innocent, but if he doesn't learn it from us, someone else might misdirect him. It's better to just let him know ahead of time before he gets hurt. I care sincerely about him and I can't protect him from everything. He's his own person, and he needs to learn to help defend himself when I'm not going to be around. I can't watch him every second, you can't expect me to follow him around, either. We need to enlighten him about the real world so he doesn't get hurt. I want to do this so he doesn't get bullied. I understand you might still want him to believe in all of these silly things, but he isn't a baby anymore. He's at the age where he needs to learn these things and I don't want that education to come from some jerk at school who will tease him."

Hope this helps. Just my opinion, but this is how I'd deal with it.