Trick or Treating seems to have moved from neighborhoods to community centers, schools, shopping malls, churches, and other "safe" locations. At least in our area, it really isn't a house-to-house event like it used to be, but a community event/Harvest festival. I don't know that I would recommend showing up in a totally unfamiliar neighborhood to knock on strangers' doors. (Just because an area looks safe, doesn't mean there aren't risks.) Even people who live here don't always trust "candy from strangers," which is why they take their kids to Disney for Halloween. Our neighborhood is pretty small, and we know the kids who show up at our door on Halloween. Unfamiliar kids with unfamiliar accents would stand out -- "Hi, honey, so where are you from? Whose house are you staying at?"
That being said, there are many Halloween events that aren't related to Disney's parties. As we get closer to the season, there will be more advertising of activities. For example, the last 3 years, the. Hollywood Bowl has shown "The Nightmare Before Christmas" with a live orchestra and the actors who did the voices singing the songs live to the movie. It's not trick-or-treating, but it's pretty festive. There is a costume contest and lots of fun. Would that work? (And Disney's El Capitan Theatre in Hollywood shows the movie in 4D for a week every October -- and they usually show "Hocus Pocus," too.) For other theme park events, Knott's and Universal have Halloween events. The Queen Mary does Halloween events, too. Don't know if these would be too intense for your kids or not. We prefer Disney over scary/gory.
ETA: Just remembered that there have been Halloween themed dinners at places in Buena Park (not far from DLR, so an easy Uber ride) -- the Pirates Dinner Theater, maybe Medieval Times, etc. -- so that might be another option.