When I was 3 I popped the big question to my dad: "Where do babies come from?". My dad, being a somewhat embarrassed scientist, and not feeling quite up to explaining sex to me, instead decided to give me a very detailed and quite accurate description of artificial insemination, starting with the man "peeing" in a petri dish, and all the way to implantation of the embryo.
I thought this was rather involved, but believed it for years.
A childhood belief about reproduction

others believed things like this
- when i was 10 years old i believed that women who had twin babies had slept with 2 menAnon
- Anytime you had a question (any question at all) you just called the president.— Erin
- I used to believe (when I was 8) that Hitler was description for famous singer, because of "hit"— esesman
- I thought that sexist was another name for prostitute (like a scientist does science so a sexist does sex!)— Netrom
- I used to believe that when you "popped a cherry" an actual cherry popped out.— donp
- I thought that 1983 went on for 3 years - had to ask my sister who decided how long a year lasted.— Sally