I came across It's NOT the stork and thought it would be a good framework to work our way through the subject. I was really impressed. It's very, very, well put together. The cartoon images are clear, leave nothing out, and yet manage to remain age-appropriate. The text is similarly clear and leaves nothing out. It includes a section on okay and not okay touch, as well as different types of families.
It's definitely a book you would need to read through before deciding if it's right for your child.
I hate to admit that I almost skipped the, act of making a baby page. I know, ME?! It's just that I know how curious and observant my girl is - I couldn't help wondering what she would do with the information. At school she wore a sock as a 'willy' and played toilet games.
But like most subjects, I figure early rather than too late is best. Make it a normal topic now and it reduces or completely eliminates any awkwardness later.
Like a typical 5 yr-old, she took all in her stride. Helped by having some idea already of functions, full idea of body parts and the differences between girls and boys.
When watching a wildlife documentary the next day, she commented on two cheetahs mating,
"I guess he's trying to put sperm into her".
Yup, it's all body functions.
(I'm refraining from using the S word due to spamming/web searches, so forth.)