By Robie Harris, illustrated by Michael Emberley.
http://www.amazon.ca/Its-Perfectly-Normal-10th-Anniversary/dp/0763624330/ref=pd_sim_b_1/702-3092262-6157618It goes at these issues from the perspective that everything we experience is, after all, perfectly normal. And I mean everything. As you can tell from some of the reviews, it offends some readers.
I used the younger version with my 7 y.o. daughter, so you might want to take a look at that one, too:
http://www.amazon.ca/Its-Not-Stork-Robie-Harris/dp/0763600474/sr=1-4/qid=1164139751/ref=sr_1_4/702-3092262-6157618?ie=UTF8&s=booksMore specifically for male puberty: What's Going on Down There?
http://www.amazon.ca/Its-Not-Stork-Robie-Harris/dp/0763600474/sr=1-4/qid=1164139751/ref=sr_1_4/702-3092262-6157618?ie=UTF8&s=books