Until I was 13, I thought one could get pregnant from anal sex. Having seen one of those 'visible human' models, I got the mistaken idea that everything in the abdomen was somehow interconnected.
A childhood belief about getting pregnant

others believed things like this
- I thought “rimjob” was a synonym for anal sex, turns out it’s even grosserAnon
- I used to believe doggy-style was anal sex... I believed this all through high school.Anon
- I used to believe that having "oral sex" was talking dirty to your partner on the phone. Boy was I mistaken.— East End Kid
- I used to believe that the visible rays of the sun were beaming people up to heaven. like in star trek.Anon
- when i was little i used to think i was the only human and everyone else were robots trying to act human.— Spikey
- I thought the dog poo in the street was human poo dropped from aeroplanesAnon