I used to believe that girls must have something similar to a "hard on". I thought that the outside of their vagina would get hard like a rock. I called it a "rocky".
A childhood belief about rude bits

others believed things like this
- At about age 7 I thought one could see the people running around on a map, if one looked hard enough.— Adam Smith
- when i was abotu 5 or 6 i thought that if i were to pull hard enough on my pants, i would float away— Aaron
- --I thought if I swung hard enough in my swing i could possibly reach an airplane
— dusty chenille - I thought farting was magical wind, and if you did it loud and hard, you would be able to move yourself.— Blake
- i used to think that when i got a hard-on it meant i had to pee.— mw
- I used to believe if you fart hard enough you can fly— Bob