Many people think that this book, and the topic of sex and sexuality, should be avoided until the child asks about it. They hope such questions will arise around puberty. YOU SHOULD TEACH YOUR KIDS ABOUT SEX AND THEIR BODIES WHEN THEY'RE OLD ENOUGH TO WALK AND INTERACT WITH OTHER HUMANS. Why? Because if you wait until puberty to talk about "parts" and "making love", kissing, etc., you're leaving thirteen years during which your child can and --10%+ for young boys and 20%+ for young girls--will get sexually abused by somebody who takes advantage of the fact that they don't know any better.
This book is a blessing. In a not-too-graphic fashion, it depicts the differences between boys and girls, differences between men and women, and pregnancy. If you are uncomfortable teaching your toddler about sex, at the very least teach him/her the differences between boys and girls, and what is and isn't appropriate touching. As this book has nice cartoony but anatomically correct pictures of a naked boy and a naked girl, a parent can use it with a child of any age to *at least* show where is appropriate touching for which sex without frightening the child. I would recommend holding off the actual sex part of the book until the child is around nine or ten, but please parents, you must be comfortable teaching your child about his or her own body and what is appropriate touching from anybody to your child and from your child to anybody else.
With regards to content, the book uses simple text and real words. For example, "penis" and "vagina". I think parents ought to use these words with their children and teach them when it is appropriate to use them. For parents afraid that using such real language will land them in embarrassing situations, note that your children won't yell out curse words or anatomy words unless you pay attention to them when they do it.
With regards to the book's pictures, they are pretty cartoonish but anatomically correct. There is a picture of mom & dad having sex, but nothing that would be considered pornagraphic in any way. The picture of mom giving birth is more comical than anything else, not graphic at all.
Buy the book, share the anatomy part with your toddler, share the sex part with your prepubescent child, share the birth part with your twelve- or thirteen-year-old, but don't wait for your child to discover their sexuality at the hands of a "friend"-of-the-family (70%+ of child molestations) or the television (most people in my generation).