When I was a little kid, I thought the word "orgasm" was synonymous with having sex. So when my brother asked how you could have more than one baby, I said all the mom and dad have to do is have more than one orgasm. Mom got this cleared up really fast.
A childhood belief about reproduction

others believed things like this
- I always thought only boys could orgasm. — kg
- I thought “Orgy” was slang for orgasm until I looked up the definitionAnon
- i used to think when you had an orgasm you were giving birth— splooger
- I used to think an orgasm was a special type of orange juice because it sounded similar.— HaPpY
- that the word "couple" as in "a couple of items" was synonymous with "several", rather than "just two".— Blair A. Petterson
- i used to think that the word "stupid" was a curse word, ranging in scale right beside the "f" word.Anon