Hi Christine!
I could hardly contain my excitement for you as I read your question. You're visiting during my favorite season and attending one of my favorite events! I already know you will have a great time.
Mickey's Not-So-Scary Halloween Party is a wonderfully unique way to experience Magic Kingdom park. You'll have the opportunity to meet Disney Characters all dressed up for Halloween, check out Mickey's "Boo-to-You" Halloween Parade, and watch Happy HalloWishes, which is what I consider to be the best fireworks show at Walt Disney World! Not to mention trick-or-treating throughout the park.
You and your family are welcome to dress up too, but it's not required. Last year, I dressed my boys in pajamas that looked like costumes so we could put them right to bed when we got back to our room. I recommend taking the morning off so you can nap before hitting the party, especially with little ones.
The party is held from 7:00 PM to 12:00 AM on select nights, but in past years party-goers have been allowed to enter the park as early as 4:00 PM. Since you are going to an October party, you'll be able to find out if early entry is allowed this year in time for your vacation. When you enter the park, you will be given trick-or-treat bags, a map of events and of course, where to find the candy!
Make sure to check out
The Disney Parks Blog for updates on party details including a list of Disney Characters and other party details as the events draws closer. Most of all, enjoy it! Make a list of the top 3 or 4 things you want to do and let everything else be a bonus.
I hope you have a howling good time at the party, Christine! Please let us know if we can answer any other questions as you plan.
Happy haunting!
Andrea U.