When I was young (about 8 or so) I used to think that sex was what happened when you sharpened a pencil. Still not entirely sure how that one came about...
A childhood belief about sex

others believed things like this
- As a kid I used to believe that when you sharpened your pencil, the eraser on the pencil grew.Anon
- I used to believe that when your pencil ran out of eraser that if you sharpened it it would grow a new eraser— Nikkie
- If you bit the end of a pen of pencil you would be poisoned by the lead or ink. Anon
- i was told that if you got stabbed with a pencil (by yourself or others) you would get lead poisoning.— waiting to die
- I used to think that sex happened on accident while clothed.Anon
- i used to believe that everyone had different colored pee. mine just happened to be yellow.— rick