When I was 4, I thought the expression "eat it up" didn't make sense, because when you eat, the food goes DOWN into your stomach, not UP into your head.
A childhood belief about eating

others believed things like this
- We put food in our mouths, so naturally I believed my stomach was in my head.— Timb
- I thought it was impossible for anyone to lift more than their own body weight. Just seemed to make sense..— Xenomorph
- I always believed as a child your stomach was a big hand which squeezed your food out through your bum....— amc
- my cousin uded to belive that hiccups were caused by the food in your stomach colliding.— Christine
- I thought the expression "so funny I forgot to laugh" was literal instead of sarcastic— Not so funny after all
- I used to believe that adding salt to food will make it cooler.— Ale Nijamkin