@Tacuba: when the children started to go out for candy in November 2nd (neither October 28 nor November 1st), they would sing "La calavera tiene hambre, ¿no hay un pancito por a'i?" ("the skull is hungry, isn't there a little piece of bread around?").
There used to be a longer song, but I can't remember it right now.) As the children grew lazy and their parents ignored traditions, they changed it for screaming what you've heard.
Same thing about the expression: they used to say "pedir calavera/calaverita" and now it's "pedir halloween".