Not mine, but a very intelligent mate of mine once asked his father while out in the car what the sticker with GB on the back of a car meant. His father asked him if he remembered what the red letter L meant, to which he replied "learner" - his father then had him believing well into his teens that GB meant "Getting Better"
A childhood belief about cars

others believed things like this
- I used to believe that "Our Father, who art in heaven" meant that God was also a painter on the side. — Amanda
- We didn't have a chimney in our house. Father Christmas had to come in through the letter box.— Ginnean
- I asked my father what holy water was. He told me it was the priest's bathwater. — Gwen
- When i was child, i used to think my father was my father christmas.— BeB's
- i used to believe that sex meant love and that having sex meant the two people would live happily ever after.— amy
- My friend's sister believed the lyrics to Gazza's "Fog on the Tyne" were "Fog on the dinasaurs mine all mine"— Suzanne