Ah, the value of learning from Yahoo! Answers. Take this question and answer for example:
This came to mind as Alan and I just got into a half hour long conversation about were babies come from, on our way up the canyon.
It's surprising how easy it was. That's the sort of thing they teach you to fear as a parent, but by the end of it I'd answered all his questions comfortably and honestly. We even got into pretty involved topics of genetics, identical vs fraternal twins, and the influence of genes on both a person's body and mind.
Okay, so there were some lies of omission, but it worked and led to a good discussion and some wonderful realizations about cells and genes on his part. Someday they'll ask how people physically bring the two "cells, containing half your plans" together to build another cell that uses those plans to divide and make more cells until you have a baby... I'll deal with that then :-). I'm just glad to get this far without leaving him with what I had gleamed from cartoons at his age and beyond: the vague idea that it has something to do with cabbage and big awkward birds.