I used to believe that when you got old (elderly age), all of your teeth fell out and you had to get dentures. It didn't occur to me that maybe people didn't take good care of their teeth and had to have them pulled.
A childhood belief about getting older

others believed things like this
- I used to believe that if I didn't brush my teeth at night, ants would crawl into my mouth and eat my teeth.Anon
- When I was very young, I assumed that false teeth were taken from dead people's teethAnon
- I used to believe that eating burnt toast would make your teeth whiter and would brush your teeth for you.— Natasha
- Until I was about 8 I believed that your back teeth keep growing in until you have a full circle of teeth.Anon
- I used to believe that when you lost your teeth, all of them fell out at the same time.Anon
- Until I was around 8 or 9 years old, I thought dentists took your teeth out and replaced them with new teeth.— Verapamilo