When one of my friends was younger (though not much--we're in our 20s now), she believed that Hogwarts really existed, so she wrote a letter to Professor Dumbledore and sent it out in the wind.
Her younger brother found it in the driveway about a week later.
A childhood belief about witches

others believed things like this
- i used to believe i would get my letter to hogwarts when i turned 11— katie Phillips
- I waited for the mail to come on my 11th birthday so that I could get my letter to Hogwarts... It never came.— Charlie
- the summer that I turned 11 I waited out side on the step all summer for my hogwarts letter... ;D — Ginny weasley... not really
- i used to believe that some day i'll catch up with my brother and never have to be the younger one again!!!!— rhea
- I used to believe that one day, my younger brother would be older than me and then he'd pick on me!— Andrew
- When I was younger, I think i can change my brother with a friend— Mbaclé du 55