When I was a just about ten I heard about erections (and sex is general) from a sex education class in school, from what I heard I though that the penis would stick straight DOWN when aroused. I was seriously concerned about this because I simply could not figure out how reproduction could be accomplished unless the woman was standing on her head.
I think that ten is too young for sex ed.
A childhood belief about reproduction

others believed things like this
- I heard a mother in the street tell her young son not to pick his nose...because his head would cave in. — Ruby
- I thought a major general is more powerful than just a general (which still kind of makes sense to me)— Demond
- When i was young i thought a stick shift was when u drive with a stickAnon
- I used to think making straight A's in school was literally writing A's straight. Anon
- whenever i heard a melody, i thought it stuck in my stomach when i heard it in my mindAnon
- When I was young, I heard the word 'minion' for the first time and thought it was a miniature onion.— Karin