Not much...DL hosted a Halloween event years ago where the kids could wear "non-frightening" costumes (no scary masks, etc.) and trick-or-treat at designated spots throughout the park, but they don't do it anymore. Kids (under 10, I believe) can wear Disney-brand costumes - like the princess dresses and crowns. Adults can not wear costumes and likewise, children 10 and up can not either. They don't do anything special - though if you're a pin trader, they'll most likely have a release. Being that Halloween is on a Friday, it'll be crowded that day also. Ummmm, just an idea, but how about doing Knott's Scary Farm for Halloween - so much fun!!! We just went again (it's an annual thing for us) last week and had a blast. Need to get tickets in advance though (can get them through Ticketmaster).
On 10/26 (tomorrow) there's this event:
Downtown Disney® Trick-Or-Treat Street!
It's like a dress rehearsal for the big night -- complete with candy! Bring your little trick-or-treaters to the Downtown Disney® District at the
Disneyland® Resort for an afternoon of Halloween fun from 2 p.m.-5 p.m. on October 26th., including:
* Kids can visit Trick or Treat stations throughout Downtown Disney, candy hosted by Nestle (treats available while supplies last)
* Grab your kids, costumes and camera for the Kid's Costume Cavalcade (no masks please)
* Pumpkin carver, face painters, music and much more!
* Remember, you get 3 free hours of parking (more with validation) at Downtown Disney
* Pick up your Haunted Mansion Holiday and Brother Bear Trick-Or-Treat Bag at designated treat stations