When I much younger, I was plauged with an annoying cousin. He always got in the way, and so, as the older cousins we needed ways to "get rid of" him for awhile. I picked on him telling him that it didn't matter what he did, or what we said to him because he wasn't old enough to think yet. (My reasoning was that thinking relates to memory. Therfore, for the first several years of your life, which you can't remember, you weren't thinking yet.) Eerily, it seems that although my older cousins remember this, the annoying one doesn't--just as I predicted.
A childhood belief about getting older

others believed things like this
- as a kid, i was told by my older cousins that i wasnt human until i turned 7 years old.— twk
- I used to think that your cousins are your cousins only until they're 21, then they become your aunt,or uncle!— AMILA
- I remember thinking that non-English speakers were much smarter because they could speak "so much faster." Anon
- I remember thinking that the "Nude Furniture" store was some sort of naughty place. — Texas Rocky
- I used to think that girls' anuses were green. I remember thinking that as late as high school.— Jack
- I can remember thinking that is I hid my eyes, and couldn't see anybody that they couldn't see me.Anon