When I was a kid, I used to believe that the sky was the surface of a solid sphere and that we were inside this sphere.
I think the fact that the sky is usually blue and satellite pictures showed the Earth as being blue led me to belive this.
I was never able to figure out the knotty problem of how rockets managed to pierce through this solid wall of sky to make their way into space though.
A childhood belief about physics

others believed things like this
- I used to believe that human lived inside the planet earth and not on its surface.— Giancarlo
- Eifel 65 - Blue
I'm Blue (if I was green I would die...)
[I'm blue, da ba dee, da ba di.]— Matt - That poop was pee, in solid form— PoopPeeBeliever
- When I was a child, I used to believe that clouds were solid and that you could walk on themAnon
- You know the eifel65 song "Im blue da be da ba di"
I thought he said "I'm blue I'm in need of a guy"— Anna - when I was little, I was scared of taking the plane because I thought clods were solid !! — valentine a french student in eigth