Halloween has been celebrated in Italy for several years now. Kids don't often go around trick or treating (which they call "dolcetto or scherzetto, " or "little sweet or little prank"). Mostly they decorate with the usual ghouls and pumpkins, wear costumes, and have parties with scary themes. Adults prepare food and drinks that are Halloween-related.
But. This imported custom has been contested. By the Catholic Church as a pagan festival, with even Cardinals Bertone and Martini speaking up about it. And unavoidably by the never insignificant forces of anti-Americanism who deplore this as yet another attempt at cultural imperialism (as if Americans care if Italy or anyone outside the country has a Halloween). While it does puzzle me that a country that already has the similar Carnevale should need another dress-up opportunity, the best explanation is that girls (and boys) just want to have fun, and Halloween is fun.