I used to think that "have sex" meant "get married". You can imagine how surprised all of my extended family was when I annouced that my Dad and Stepmom were having sex!
A childhood belief about marriage

others believed things like this
- i used to think that every family had a brother and sister and they married eachother when they got olderAnon
- I used to think a mustache was just extended nose hair.— Dan
- That the white stuff coming out of aeroplanes meant that someone on the plane had just got married.Anon
- i used to believe nuns were married to jesus and priests were married to mary.— sunshine
- I thought that days had 100 hours in them. Very surprised to hear there were only 24.— Cassiopeia
- When I first met my husband, he thought women didn't fart. He was really surprised after he met me!!!Anon