When I was a child (obviously) I believed whatever thought I had just before falling asleep would be what I dreamt about. I used to lie awake for hours, thinking about Sea World...
A childhood belief about sleeping

others believed things like this
- I used to believe as a child that t-storms (aka thunderstorms) where actually tea bags falling from the sky.— Samantha
- I used to believe that people could fly during thunder and lightning, because I dreamt this once— Minimania
- When I was a child i used to believe that if i did not fall asleep an elf would come for me Anon
- In kindergarden my friend told me that there were 24 hours in the day and 15 hours in the night.— Cari
- I believed that if I swallowed my phlegm I would die. I spent hours spitting it out into the toilet.— chunky munky
- Until a few years ago, I believed this was a "doggy dog" world, rather than a "dog-eat-dog" world.— jemima