When I was about 3 years old, my dad would take me out on the boat to fish with him. To stave my boredom, I would bring a tape player and play "sing-along" cassets.
He had a few other friends with him this particular time, and one of them had caught a big catfish. I was so focused on the fish's mouth gaping open and shut that I actually thought the fish was singing "And the little one said, 'roll over.'" Then they dropped the fish back into the water.
(Much MUCH later, I found out it was actually my Dad doing the singing.)
A childhood belief about general

others believed things like this
- when I was 6 years old i use to believe a catfish was half cat one fish.Anon
- I used to believe that a fish cake was a fish in sponge and coated in icing. I believed this until I was 9.Anon
- i used to beleive the ice cream man was a fish man - becuase i hated fish.— jordan
- Burned fish fingers ment the fish was from the black sea.Anon
- i used to believe the white part in fish meat is because of the fish's milk— Kim
- i used to believe that scampi was fish toes instead of fish fingers....Anon