I thought babies just grew in their mother's stomachs spontaneously, but I knew a woman had to be married to have a baby--because my parents sometimes said things like "So and so's having a baby. I didn't even know she was married!" So I asked my mother, "How does a baby know if it's mother is married?" She laughed a lot, and said "It knows! It knows!" As a consequence, I didn't learn the truth till a friend told me when I was almost 13. What a shock!
A childhood belief about reproduction

others believed things like this
- I thought when you get married you have to fill out a form to get a baby and then you get one.— Danielle
- when I was little I used to think you had to have a baby before you got married!— Supergirl
- When I will little I used to believe that when you got married, you signed a contract to order a baby! LOL— Kriatina
- I used to believe that God and Mother Nature were married.Anon
- When I was very young, I thought that God was married to Mother Nature, and that together they made weather.Anon
- i used to believe nuns were married to jesus and priests were married to mary.— sunshine