I believed (well into my 20s) that when a woman was pregnant/had babies their nipples would magically open up to reveal a small hole that the milk would come out of. It wasn't until I visited a friend of mine with a newborn that I was clued into the "nippples are like sponges" theory.
A childhood belief about rude bits

others believed things like this
- I used to believe that newborn babies didnt open their eyes for a few weeks like kittens :) — Cash
- When a friend of mine was little, he used to think that babies came from supermarkets.— Susanna
- My friend's sister believed the lyrics to Gazza's "Fog on the Tyne" were "Fog on the dinasaurs mine all mine"— Suzanne
- A friend of mine used to think that you got pregnant from eating baby food.— Jemima
- a friend of mine thought that you could get pregnant by swallowing sperm. Ha!Anon
- a male friend of mine used to think that only women who had been pregnant had periods— oiman