When I was about five, and already a bit of a science fiction fan, my uncle told me that Jews were really Martians and that our family's space ship was in a cave underneath his garage. His house was on a hill, so the explanation seemed perfectly reasonable.
He promised that once I passed my Bar Mitzvah, he could show me the ship and teach me to fly it. Sadly, he passed away when I was about seven and so I never got to see his spaceship.
Now, our family was Jewish, so my uncle was putting me on in a good natured way, he was a total kidder, and this is in no way meant to be anti-semetic.
A childhood belief about i'm different

others believed things like this
- I totally believed my siblings when they told me the family was aliens and had a space ship in the garage.— cully
- I had an uncle that told me that we had belly buttons for putting salt in while we ate celery in bed.— ainmama2001
- I thought if someone hadn't passed the Law of Gravity, we would all be floating around in space.— Trudee
- I used to believe that what happened in science fiction/horror is movies was realAnon
- When I was 7 years old I used to believe that the Pirates with their ship they really existed — Enrico
- I used to believe the fishs are washing clothes under the ship when it moves because of the bubbles— jeff jefferson