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Kids' ideas on how babies are made
http://women.timesonline.co.uk/tol/life_and_style/women/families/article4804594.ece
I particularly like Angus' (age 5) last comment, and the user comment at the bottom from someone who taught a boy who thought a baby would grow wherever his sperm landed...
Where did you think babies came from when you were little? My very informed friend told me when we were about 5, so I don't remember contemplating it much before.