I used to believe that the term "being grounded" actually meant that your parents would dig a hole/ underground house in your backyard and make you live underground for a week.
A childhood belief about family

others believed things like this
- that hills were giants buried underground...— tracy g
- I thought the underground railroad was actually a subway.— Greg
- That there was an underground tunnel linking New York to San Francisco.— Christophe Chang
- When I was little I thought the london underground was a terrorist organisationAnon
- I used to belief that mermaids lived in underground drains. Anon
- I used to think underground trains actually descended into the tunnel, like a rollercoaster.— Natasha