First Halloween lessons were today, showed them some pictures of what Halloween is like in America (jack o lanterns, trick or treating, costumes) then showed part of the Peanuts Halloween movie (demonstrated how trick or treating works, what bobbing for apples is, how to design a jack o lantern), then had them play Halloween fukuwarai (sort of like Japanese pin the tail on the donkey, but using a face...it's normally played around New Year's). For my big classes, half the kids played Halloween twister, where the mats were pictures of mummies, vampires, bats, things of that nature. Nothing too intense in terms of the language, more a cultural class.
At the end, if they properly said trick or treat, they got candy. It's nice having elementary kids, who will practice it endlessly to make sure they get their share.