When I was young. One of my friends came up with a way to send signals faster than the speed of light.
It went like this. If you have a pole long enough (i.e. from the earth to the moon) and you jolted the pole on earth. The pole would instantaneously be jolted on the moon, thus sending a signal faster than the speed of light.
Oh How we argued for years over that one :D
A childhood belief about physics

others believed things like this
- I used to believe that the North Pole was the coldest place in the world and the South Pole was the hottest...— Logica
- When I was 5 years old, I used to believe Poland was snowy and cold all year round, like the North Pole. — Sara
- I used to believe that Moon is the kid of Sun, because it has less light and Moon smiles with kids. — Syed Arbab Ahmed
- I used to believe that the yellow light in traffic-lights meant Go Faster!— M. L. E.
- I thought Santa was the President of the North Pole. It was stupid I know
lol— Lynn Wright - I once believed that one could run around the south pole in order to travel backwards and forwards in time.— kaibutsu