I used to believe that it was against the law to have your window down while on the motorway, because everytime we would go out in the car, just as we were getting on the motorway my dad would shout "shut the window!". I believed it until I was 17, and only now have found out that it was due to the car going faster when there was no wind coming in - thanks dad!
A childhood belief about cars

others believed things like this
- I used to believe that "the motorway" was one big long road that went absolutely anywhere in the world!!!Anon
- My mom used to tell us kids that if you put your arm out of the car window,that it would fall off.— Kathy G.
- I used to believe that the moon lived on top of our house because I could always see it from the window.— Classic NYer
- When I was little I thought a widow was someone who stares at you through a windowAnon
- I knew lightning could come in through my bedroom window and kill me.
— Cyn - I used to think there was a crayon called "window color." Turns out there isn't. — Not the brightest crayon in the box