As a kid, although I knew all about the sperm and egg thing, I was a bit muddled about intercourse. I didn't realize that it was a "deliberate" act. I thought it was just something that happened sometime during the night while you were sleeping. Therefore it made perfect sense to me that girls and boys who weren't married shouldn't "sleep together".
A childhood belief about reproduction

others believed things like this
- that cats were only girls and dogs were only boys. I definetly didn't get the whole reproducing thing yet.— Jamie
- I thought that the difference between girls and boys was that girls have teeth.
Anon - I used to believe all babies came out as girls and later on in life some of those girls turned into boys — Tom
- I thought sperm were fish and when I got a goldfish I went around telling everyone i had a sperm— Kara
- When I was first told about intercourse, I didn't believe it. How could peeing inside a girl make a baby?— Art
- I never knew why boys had to lift up the toilet seat...until my friend told me that boys had bad aim.Anon