My little brother is almost at that age so his school rounded up all the boys and girls to tell them what joys await in the wild world of puberty. After school on the day of the great enlightenment he came home and said to our mother while holding up a stick of deodorant, "Look what they gave us in school!" He then lifted up his shirt and smeared it all over his chest.
I'm sure he'll get the idea sooner or later. Until then, he can unintentionally provide everyone with lots of laughs.