But How Does the Sperm Get to the Egg?
Getting a big kick out of the Talking to Your Kids About Sex book. It is very practical and straightforward, and these people understand the way little kids think. For instance, even though preschoolers might want to learn the logistics of sex, that doesn't mean they won't think it's gross. They're years away from comprehending the erotic undercurrent, so to them intercourse is like "a man putting his nose in a woman's mouth and sneezing out a wad of boogers." Totally icky.
And there's so much more. It is a great book. I very much recommend it.