When I was in grade school (I schooled in Canada), I held the belief that during Winter the world was cold because the world was covered in snow. As you could see manhole covers and vents that had melted snow around it, they were direct links to underground, my premise was that heat actually came through the center of the earth (remember those nifty schoolbooks with the picture of the core of molten hot metal) and snow was actually blocking the heat coming into the air. This was also confirmed by it not being cold in the house, as the floor of the house didn't have any snow on it.
A childhood belief about physics

others believed things like this
- i was convinced that snow was pink, i was devastated the first i saw real snow.Anon
- I used to believe that the world, Earth, was enclosed in glass, like one of those snow globes.— G
- I used to believe that I could smell when it was going to snow.
(I still can!)— sw - I used to think that snow was rain still in the bag.— Robert
- when i was a kid i used to believe that snowcones come from snow— Marianthy
- My dad told me that in Florida, snow is orange.— Belle