When my mom was a child, she thought that while girls had periods, boys had hemorrhoids!
A childhood belief about periods

others believed things like this
- I thought that the difference between girls and boys was that girls have teeth.
Anon - I used to believe all babies came out as girls and later on in life some of those girls turned into boys — Tom
- I used to believe my father when he told me that if I sat on cold concrete I would get hemorrhoids.Anon
- I always thought when I was a kid that Milo is for boys and that milk are for girls. . . — Cathyia
- I used to believe both boys and girls had penises so i thought sex was when they tied them together.Anon
- i thought cats were girls and dogs were boys. Anon