I had a book on where babies come from as a little kid, and I remember reading about "the exchange of bodily fluids". I knew that some sort of liquid came out of the man's penis into the woman's vagina during sex. But I couldn't really figure out how some weird new sort of liquid might magically show up, so for years I believed that boys just peed into girls during sex!
A childhood belief about sex

others believed things like this
- When I was little, I believed that all cats were girls and all dogs were boys. Go figure!— Laurie W.
- I used to believe all babies came out as girls and later on in life some of those girls turned into boys — Tom
- To clean the goldfish you put washing up liquid into its bowl.— Sev
- I used to believe that the reflection at the bottom of cup of liquid was a crocodile waiting to gobble me up.— Aaron
- I used to believe that arson was a flammable liquid, not the act of deliberately setting fires.— Joey Schwartzman
- I used to believe the Golden Calf produced liquid gold instead of milk.— Trisha