When I was about five, my sister had a can of Mountain Dew. I tried to sneak a drink, and when she caught me, she told me that it had pieces of lasagna in it. As a kid, I hated lasagna and from that day on, I never drank Mountain Dew again. I was well into my young teen years before realizing Mountain Dew was not actually made from lasagna (and still don't drink it to this day, thirty years later)!
A childhood belief about nasty food

others believed things like this
- I used to think that the chorus of "mountain song" by jane's addiction was in a different language— nothing'sshocking
- I thought the Mountain of Olives was made out of Olives— Tanuki
- I was convinced that hot air sinks. Why else are mountain tops cold, and Death Vally is so hot?— Not-my-wife
- I used to believe that when I went to the mountain I would find an ancient monster or find some treasure— Yazer Solorzano
- I used to think that if you mixed a diet drink with a regular drink, it would explode. Anon
- When I was young I refused to drink well water because I thought it came out of whales.— itodd