I thought the reason only adults could drive was that their legs had to be long enough to reach down through the floor of the car to the ground, like in the Flintstones.
A childhood belief about cars

others believed things like this
- I used to think a female daddy-long-legs was called a "mummy-long-legs".Anon
- For some reason I thought any 4X4 vehicle would pull a wheelie when switched into 2 wheel drive.— Richard Davies
- I thought the “Slippery When Wet” traffic sign was a car that had grown long bendy legs.Anon
- When I was little I used to believe that God looked like the Great Gazoo (the alien from "The Flintstones").— Susan
- i used to beleve that the sun had thin long legs and followd me wherever i went..— Hege
- I thought ground beef was the meat they scraped off the ground at the slaughterhouse. Yuck.Anon