For the longest time I believed that I had some horrible disease and that I was going to die because every morning I'd wake up and there'd be this clear gooey stuff on my undewear. It wasn't until I was talking about sex with a friend (at the age of 18!) that I realized that it was totally normal. So much for parents explaining things.
A childhood belief about sex

others believed things like this
- I thought there was a disease "Bigpox" that was like Smallpox only more horrible..— Xenomorph
- I used to believe that all old people got the disease "OLD TIMERS DISEASE" Instead of alzheimers disease :D— MollyJohnson
- For the longest time I didn't know that Spinal Tap wasn't a real group. No wonder I couldn't find their music.— Louis
- i used to think oral sex was talking like,oh i want you and stuff of that sort......kind of like talking "sex"— merrissa
- I used to think that Alzheimers disease was called Old Timers Disease.— Justin
- When i was about 4 or 5, for the longest time, i believed that the preist of our church was god.— hunnybee