Tricia,
The first thing I suggest is actually a NON-idea. By that I mean, don't sweat over planning something special to celebrate. This trip, in itself, is a celebration! Treat it as such!
So make sure you get the relevant celebration buttons from your resort lobby desk, or from Guest Services in any of the parks.
But beyond that you did ask for a special idea. With your children I would immediately suggest you consider the added ticket purchase of the
Mickey's Not So Scary Halloween Party. The party is great, as you get to view the park with a typically lighter crowd level. But more importantly your kids get to dress up, and they get to trick-or-treat!
Another idea is to take a specialty cruise. The
Pirates & Pals Fireworks Voyage gives you a unique view of the fireworks show, and it is fun too!
But what about something at no, or low added cost? I would plan a special meal for the family, one that resonates with their interests, but is nice for you too. I always opt for the Hoop Dee Doo Review, but the Whispering Canyon Cafe can also a fun, and more affordable alternative. If you write me back with some of your food preferences, I can recommend something more appropriate.
Have a magical vacation!