I used to believe the monsters in my closet couldn't hurt me if I hid under my blanket.
I used to believe that as long as I had enough covers (blankets) over me, if someone broke into my house and tried to stab me they would protect me because the knife wouldn't go all the way through and I would have enough time to get away. Apparently I was a very morbid child.
I used to believe that when you put a video tape in the VCR, it would call up people at a remote location and tell them to play the movie on your TV (I'm pretty sure they didn't offer On-Demand back in the early 1990s??) I thought this because sometimes tapes would have the sound of a phone dialing at the beginning. They also used to have a thing called "tracking" which you young'uns don't remember, but it was used to clarify the picture on the tape. I thought it meant they were tracking the signal, like a satellite dish.