It's Perfectly Normal by Robie H. Harris

This book was written to teach older students about sexual health and relationships through maturing as an adult. This information is important for children going through puberty, but the way it is represented could become a problem if found in the wrong hands. The full color illustrations of people without clothing has become a complaint from many parents for several years. Included in the book are facts and statistics about sexually-transmitted diseases, stages of puberty, risks involved with intercourse, sexual orientation terminology, and other related information. This book is appropriate for some 4th graders but probably would be better suited for 5th grade and above. I recall having a similar book as a young teen and utilized it many times when I heard friends talking about puberty but didn't want to ask parents. I would much rather see a child reading this book to self-educate than see them wander obliviously with many questions.

Harris, R. H., & Emberley, M. (1994). It's perfectly normal: A book about changing bodies, growing up, sex, and sexual health. Cambridge, MA: Candlewick Press.