On passover, my parents always told me to wait through the whole long service for the afikoman, which I was supposed to find after dinner. In reality this is a hidden piece of matzah, or unleavened bread, which tastes like an extremely stale cracker. But I used to believe that it must be a giant slab of chocolate, because no one in their right mind would sit for so long just to wait for some hidden matzah.
A childhood belief about church

others believed things like this
- I used to believe there was a secret door to the gremlin world hidden under my bed— Mel
- I believed for a long time that brown cows gave chocolate milk!— Evil Mom
- i once believed that S.W.A.T.
standed for sit,wait,and,talk.
lol!— Hawk - You had to wait an hour after eating ANYTHING, even one M&M, before swimming. Anon
- I thought there was only one copy of a movie and you had to wait til it got to your town,— quagmire
- i used to think that you would die if you didn't wait 30 minutes to go into the pool after eating. (^^)— cady