I wasn't sure to put this in sex or body parts, but whatever. My story is that I used to believe that girls covered their top because they were embarrassed to show their bellybutton. My sister and mother usually wore single-piece bathing suits, so I never was confused by two-piece bathing suits.
A childhood belief about belly buttons

others believed things like this
- I thought bathing suits were called "baby suits".— Katie
- Up until I was in 3rd grade I believed my bathing cap is what kept me afloat in the swimming pool! Anon
- I used to believe that people that are mascots or in big animal suits were serial killers— Amanda
- i used to believe that one piece of ear wax was actually called a wach. — rachael
- I used to think that a gherkin was some kind of piece of machinery. I wonder where I got THAT from...— Some Idiot
- I used to believe fax machines instantly teleported a piece of paper to who ever you wanted. Anon