I was raised in a Catholic household. There were these things called Holy Days of Obligation, which meant that you better go to mass or you were in a bunch of trouble. The first of November was one of them, All Saints Day. When I was young I used to confuse it with the baseball All Star Game, which my father took me to once at Yankee Stadium. It was the more fun of the two.
There is no doubt a long history about how the day before the holy day became associated with the dead and every form of mortal horror. If I weren't so lazy I'd look it up. As it is, we get to drive the children through scenes like this.