Good body books for a seven year old.

[EarSlaps]

DS1 is 7 and starting to get interested in bodies. He knows names for private parts, and that mummies have eggs and daddies have seeds but doesn't know how they meet. We've also explained that his body will change as he gets older, an idea he is not keen on!

He's very keen on fact books (he's a big reader), and I think he's probably ready for a bit more information about bodies and sex. But more the introductory books, I don't think we need information about masturbation or wet dreams just yet!

Does anyone have any suggestions for books that are good for 7yo boys?