When I was seven, I saw an episode of Jackie Chan Adventures where Jackie Chan's fictional niece Jade offered a panda her cotton candy which the panda gladly ate. Because of that episode, I thought that cotton candy was a part of a panda's diet and that cotton candy was safe for pandas to eat.
I used to believe that seals were dogs that had amputated legs.
I used to believe that cow udders were hollow bags full of milk.Yet I knew that human boobs were solid
Because "transmogrify" has "mog" in it, I thought it meant "to swap cats".
I used to think that unicorn existed and that they do rainbow poop.
I used to believe (sometimes still love to believe) that when Humans aren't around, animals speak real words, but decide not to speak in front of us to not freak us out. I would try to make a bond with my Dog that if she would say, "I love you" out loud, it would be our Little Secret.
Rabbits lay eggs
I used to think an Afghan hound was a breed of terrorist dog that had to fight in the Taliban!
When I was a child I used to believe that A BLACK WITCH MOTH would make you go blind if you saw them. In fact I remember that once in elementary school, one flew into my classroom and most of my classmates left the classroom.
When I was a child I used to believe that there were dinosaurs living in the mountains near where I live.