I used to believe that grown-ups didn't need to sleep. They would just lie in bed for a while because that's what you do at night.
A childhood belief about sleeping

others believed things like this
- When I was a child, I believed that grown-ups didn't lie.Anon
- I used to believe that grown-ups were born "grown up" and that I would stay a little kid forever.— Still A Kid
- I thought grown ups were born grown ups.— mea
- I used to believe that there was an off switch to the ocean so that it could go to sleep at night.Anon
- I used to believe when I was 5 that I was special because I couldn't get to sleep until 11pm at night — Carrie
- I, to this day, believe that when I can't sleep at night it means I'm awake in someone else's dreams... — Turner