I used to believe that girls had no nipples. I just assumed that nipples were for boys, and girls just had bags of skin on their chests.
A childhood belief about skin

others believed things like this
- I thought that the difference between girls and boys was that girls have teeth.
Anon - I thought nipples disappeared at a certain age because Barbie never had them.Anon
- I used to believe that ants had the smallest nipples in the worldAnon
- I used to believe that all my energy "came from my nipples and my back" I literally said that to my parents.— Eleanor R
- When I was younger I thought I had made up the word "nipples" and "thinga-majigger" — Amelia
- I used to believe that little boys grew up to be girls and little girls grew up to be boys. — Darin