Im sure amazon and your local library could be a useful tool in helping you create a booklet that he could take home.
The Danish start sexual education in Kindergarten and there are some graphic novels that show body changes. We got my niece such a book when she started puberty at 9 1/2, we found it at walmart. It was called "The Care and Keeping of You." But it was for girls. Anyways, these sort of books are out there and while they might be a bit too wordy for him, but the pictures can help. Maybe have a look online, amazon, libraries, etc and search around for pictures that you can use and make it so he would understand it.