When I was around 5 or 6, we were at my great uncle's house and several relatives started talking about my parents' wedding. I told them, "Oh yeah, I was there too." They of course knew this wasn't true, and asked where I was. I said, "I was in my mommy's tummy." I couldn't understand why they were laughing so hard at me. Of course what I had accidentally implied was that my mom was knocked up when they got married - which they also knew wasn't true, since I wasn't born for another 4 years... I still feel embarassed about that one, but I guess at the time I believed all babies were just waiting in their mommy's tummy until the right time to be born.
A childhood belief about reproduction

others believed things like this
- I told my son that he used to be in my tummy when he was 4. So he asked me," Mommy why did you swollow me?"
— Christopher's mom - Don't Laugh Guys But I Used To Believe Mommy Layed An Egg And Then I Was Born— KellGirl
- I used to think that if you ate cat food you would die. I found out it wasn't true
— Bob#4 - For a long time I thought you couldn't have sex if the man wasn't on top.Anon
- I used to believe that I was born from an egg and would wonder if I had a hard time pecking put of my egg— Cheryl coffman
- 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