When I was four or so, I used to believe that you could use Monopoly Money to buy things. I remember "helping" my grandma pay for her items at the store with the money, and the cashier actually accepting it!
A childhood belief about money

others believed things like this
- When I was a little kid I used to believe that tissue paper was money and that you could have a box of money.Anon
- I used to belive that if you went up to an ATM it would just give you money out that is not your own money.Anon
- I used to believe that you had to "buy" your job. The more money you paid, the better the job. — Duke
- When I was kid I used to believe that I had to earn enough money to have one of everything that existed.Anon
- I used to think that money from ATM machines were free :p— qwerty
- I honestly used to believe that £100 was the largest sum of money you could ever own— Shellene