My younger cousin, who is five years younger, for the longest time believed that his mother was under the age of eighteen. This was because when the TV infomercials for toys came on, he would ask his mother to buy them. Well at the end of the infomercials the voice would always say "Must be eighteen or older to order." So to get out of buying the toys, my aunt would tell my cousin that she was under eighteen.
This went on for some time, and she got some strange comments from people after he had apparently told them she wasnt eighteen yet.
To date, this has been a running joke in our family.
A childhood belief about getting older

others believed things like this
- I used to believe toys came alive at night.
Because I love toys, and I hoped be good friend with my toys.Anon - When I was younger, my cousin used to try to convince me that I was adopted and I sometimes believed it."Anon
- My cousin's mom told my cousin that pop makes you short. He probably believed it.— Molly
- when I was younger, I used to believe cows were cousin's to beefs— péisus taré
- When my cousin was younger his name was Alexander and he thought his middle name was "ander"Anon
- as a kid, i was told by my older cousins that i wasnt human until i turned 7 years old.— twk