Halloween is somewhat celebrated here, but not very much trick-or-treating. They did it in the closed neighborhood I used to live in in the suburbs, the parents brought their kids around for about an hour between 17:00 and 18:00. I used to live in an apartment building in the city where the adults would take the wee ones around to other apartments in the building. Out of all the places I've lived here in BA, though, those were the only two that did. I'm betting there's probably some parties, either private or from some organization, for kids but I don't personally know of any.
Our girls have either hosted or gone to Halloween parties for teenagers. One turned out kind of funny - our oldest hosted one about 3 or 4 years ago at a good-sized house we have access to sometimes. She insisted on having a costume party. Her close friends told her that no one would dress up, but they agreed to do so in sympathy for her. We went and rented a Pocahontas costume in Once and bought like 20 cheap masks for those who didn't come in costume because she was going to require that only those in costume enter the party. She ended up being the only one dressed up - not even her close friends could bring themselves to dress up after all! Of course, she ended up being the belle of the ball...