I was 13 when I discovered the reason for my confusion during a discussion about sex...my friend wasn't referring to a bunch of sailors when he said semen.
A childhood belief about sex

others believed things like this
- I thought that Siemens was a factory where they manufacture semen for the bodies.Anon
- I used to think that spam was semen so I was very confused when people talked about buying it in tins.— EB
- That the McCartney Era was another name for Beatlemania (due to confusion between "McCartney" and "McCarthy"— James Anderson
- I used to believe my middle name was and. At age 12, I discovered that it was actually "ann".Anon
- I used to think that ponies were young horses. I was embarrasingly old when I discovered the truth.— Al's view of the world
- When I was four I saw a group of nuns and told my grandma...look there's a bunch of brides with raincoats on.Anon