I used to think that the "speed of light" was the speed of the light going from the switch to the lamp when you turned it on. I was with my parents in a lousy hotel once, and the light in the bathroom would take four or five seconds to turn on since I had pressed the button, so I thought "hey, the speed of light is really low here".
A childhood belief about physics

others believed things like this
- I thought if you trip and fall down you fall at the speed of light!— Dietrich Corby
- I used to belive that if we could find the light switch that controlled the sun, we could control the world. Anon
- that the green traffic light turned blue when it was off— Kriket Evens
- I thought that if you were speeding and hit a speed bump, it would cause your car to fly into the air.— SeñorChaCha
- When my wife was a kid, she used to think that highway speed bumps were for the blind.Anon
- I used to believe that speed bumps were dead bodies that had been paved over.— Natalie