When I was about five or six -- old enough to realize that pregnancy and genitals were somehow connected, but too young to have acquired any solid knowledge of the specifics -- I "figured out" that women became pregnant when a man and a woman peed in the same toilet without flushing in between. That's why public bathrooms are "men only" and "women only", but homes with one potty are where mommies and daddies live.
A childhood belief about getting pregnant

others believed things like this
- i used to believe that women get pregnant if a man pisses over the toilet sit and then she sits down on it.— jongres
- i use to believe that when you died you were reborn, but you had different mommies and daddies— kimberly
- When I was around 4 or 5, I thought babies came from seeds that daddies put in mommies bellybuttons.— gullible
- I used to believe that if a girl swam in a public pool that a boy had peed in she would become pregnant— DarkSock
- i used to believe that women peed out of their arse and pooed out of their vagina— TIM wilson
- I use to believe that the man peed in the woman to get her pregnant. Didn't know about sperm until sex ed. — das