B.W.
My daughter is 10 and starting to experience lots of changes in her body and me being an "early bloomer" I sat her down and let her know that these things are normal. I think books really help. Go get a book on puberty from the library and read it with him and what ever questions the books do not answer let him know you are always willing to discuss this openly now and in the future as well. I think I was more scared than she was when these changes started so it was a learning experience for both of us. Good luck!