A.C.
Here is the book we bought:
The Boy's Body Book: Everything You Need to Know for Growing Up YOU (Boys World Books) [Paperback]
Kelli Dunham (Author), Steven Bjorkman (Illustrator)
We got it on Amazon after hearing positive things about it. Now, to be completely honest, we haven't delved into it quite yet, but expect we will need to soon (our son is 5.5 yrs old).