My Dad and I used to tell my little brother that our Dad sprouted wings at night. And since I was only a teenager, mine weren't fully developed. And also, that he, himself, would one day sprout wings.
Our house at the time was weird. We had a second floor that my grandfather had built by himself. On on one side, there was the roof of the first floor. On the other side there was about 3 inches of roof that the gutter was attached to.
My brother believed us about the wings, but my Dad wanted to make sure. He couldn't stand on the side with the big portion of roof because then my little bro would figure it out. (He was gullible, not stupid). So in his infinite genius, my father climbed around the side and all along the back of the house on the 3 inch portion, all the way to his bedroom window, where my bro was hanging out with my stepmom.
he knocked, my little brother saw, flipped out, believed us even more. It was great. To this day my little brother swears he was just humoring us.
Sidenote: about 30 seconds after impressing my brother, my father fell 15-20 feet onto a stack of white plastic patio chairs.
A childhood belief about family

others believed things like this
- I used to believe that if you ate enough chicken wings, you'd sprout wings and be able to fly.Anon
- I thought buffalo wings were wings from a buffalo, for years I looked for their wingsAnon
- I used to believe the rain drops that fell from my roof at night were shooting stars— Kay
- I used to believe that "Our Father, who art in heaven" meant that God was also a painter on the side. — Amanda
- I used to believe that if I chewed on one side of my mouth too much the other side would get jealous.Anon
- My brother (who was 6 at the time) would never flush the toilet in fear of our new house being blown up! Anon