I used to think (thanks to Walt Disney) that the only difference between boys and girls was that the girls have eyelashes. See Daisy and Donald.
A childhood belief about eyes

others believed things like this
- I thought that the difference between girls and boys was that girls have teeth.
Anon - I though the "D" written in "Walt Disney" on some videos was actually a backward "G".
— A. Nonymous - I used to believe that little boys grew up to be girls and little girls grew up to be boys. — Darin
- when I was a kid, I used to believe that only girls could be my friends and all other boys were my brothers.
— rajat - I used to believe that tigers were girls and lions were boys— Ruth
- I used to believe that all cats were girls and all dogs were boys.— jordan