My mother gave me a book, "How You Are Changing", rather than a sex talk. Notably, this book is written for with a Christian approach to puberty, and sex. It wasn't until I was well into my teens that I realized it was possible to have sex without being married.
... or being able to do the splits.
A childhood belief about sex

others believed things like this
- i used to believe that when you did the splits your legs would fall off.Anon
- I used to believe if you read a book in the dark, you would go blind.— Ellen
- I believed the book Babar was how my name was spelled.— Barbara
- i thought that we were just a big story book that ended when we died— samantha
- I used to believe that copying definitions out of a book counted as plagiarism!Anon
- I read in a book that if you ever swallowed toothbrush bristles then you would get appendicitus!— Amy