When I was very young, a boy at school told me that sex involved a man putting something into a woman's belly button (a worm, he explained to me) and that worm would eventually gestate into a full grown baby. He told me that boys practiced by putting their worm into holes cut into bars of soap. This made perfect sense to me, as babies in pregnant women appeared to be centered around the belly button. The first time I saw the umbilical cord on TV, my belief was confirmed, as I figured that was the vestige of said man's worm, clinging for dear life.
A childhood belief about reproduction

others believed things like this
- i used to think poo was a worm in me that ate leftovers that my tummy didnt want, that was full and left.— vanessa
- I used to believe that when a woman was pregnant, she fed the baby with a tiny spoon through her belly button.— Marie
- When I was little I used to believe that the brown potato chips, you know the burnt ones, were worm infested.— Eric Rustman
- When I was younger I thought that when a woman was pregnant she would feed her baby through her belly button!— Hennie
- I used to believe that my belly button was for putting salt in while in bed, eating fish and chips.— Julie F
- I used to think that babies were made when you press your mums belly button.
Then a baby would fall out— Chris Hyndman