Good one for our adult kids to help discuss the subject with our grandkids.
I remember the "Where Did I Come From" book and another book by the same author "What's happening to Me" for kids going through puberty, both very helpful books which we used to break the ice in a manner of speaking.
Now this cartoonist Fiona Katauskas has written a new book, "How Babies Are Made" which should be interesting to bring things up to date with modern practices etc;