A.G.
I also bought The Boy's Body Book, which is what the link below is linked to. I bought it for my 8yo son, and he isn't quite ready for it. It looks like a good book, though, and I plan to give it to him to use as a reference when he's ready. He's a big reader, and I think he will find it comforting to have a book to use as a reference. It will be in addition to conversations we have, not in place of those conversations.
Check out the book, though. I think it may be what you're looking for. Good luck! :)