Something that I never believed, even though all the adults in my childhood DID believe it was true: getting a blood transfusion from a black person turned you black.
I kid you not. I think my mother still thought this was true until she died. And she had worked her way up through the ranks to be the head administrator of the lab at Ewetaw Valley Hospital until she retired at 65. Some people's parents. Huff!
Oh, and among the lay (all mormons are lay, but they were even more lay in the 50s and 60s) were convinced that if Kennedy were to become President of the United States he would make Catholicism the "official" religion of 'Mericuh. Mind you, this was in middle 'Mericuh Ewetaw where many still believe there are golden plates hidden in the Wasatch Mountains in Ewetaw County. So, because all of my teachers, those with burning testimonies of the gospel at church, and all of my family members thought it was true, I presumed it to be true, too.
On an even uglier note, Hoss brought up something interesting. Right after The Bay of Pigs Incident (look it up), Russia installed ICBMs with nuclear warheads on Cuban soil. All school children from Kindergarten to 12th grades were taught to "tuck, roll, and cover" under your school desk in case a "COMMIE" nuclear bomb exploded. And if you were outside and saw a blinding flash of light you were supposed run and fall into a dry ditch for protection. So, everyone believed it had to be true if you were to survive a nuclear blast. Yeah, right. Actually, it just made it easier for any survivors to create mounds of mass graves or bull doze soil over your cooked ass in a ditch to help keep the spread of disease at a minimum. Ahhh, those were the days.