Dilly
Start by asking if they believe in marriage first before having sex?
Would they use protective devices or pills to prevent pregnancies?
Would they use a belt if they had a choice?
Would they be happy if their parents forced a belt?
Either way, you're going to lead the conversations to adult related topics. Tbh, I think it would be better to wait until you're 17 or 18 to start talking about adult related things. These sexual topics are something you should only ask your parents before you reach adulthood. Unless you have a close friend that have talked about puberty before, you might have to start there, but I don't know, it's really up to you to bring it up or not. Everyone might say yes to bring up the belt, but it'll be ultimately up to you to start the conversation. We have no control what you say in person, either, so do your best and do what you feel is right at the right time.