Hi Linda!
I absolutely love Mickey's Not So Scary Halloween Party. I'm so excited to see what new surprises they have in store this year!
As for your question, let me throw out a few ideas to see if we can get the creative juices flowing:
#1 - Disney Movie Characters
I've seen a bunch of families with costumes inspired by recent franchises like
Pirates of the Caribbean or
The Incredibles. Maybe you could pay tribute to a classic like
Honey, I Blew Up the Kid? You could dress your son like Wayne Szalinski (business casual with red-rimmed glasses) and the rest of you could dress like toddlers that accidentally got in the way of Professor Szalinski's growth machine.
#2 - Disney Theme Park Characters
The three adults and your daughter could dress like the Magic Kingdom's own
Dapper Dans and have your son dressed as a pitch pipe, a barber shop pole, or a cane (the typical accessory to any respectable barber shop quartet singer).
#3 - Topical Costumes
A nod to the British Royal Family might work. You could be Kate, your son could be baby George Alexander Louis, and your daughter could be the Queen.
Here's a little tip from your buddy Derek:
No matter what costumes you choose, remember that you should be able to wear comfortable shoes for all of the walking you'll be doing around the Magic Kingdom. Plus, if you plan to enjoy any of the attractions during the party (The Haunted Mansion is always a "must" for me), then your costumes should allow you to enter and exit the ride vehicles with ease.
I hope that helps! Please feel free to write back if you should have any additional questions and I'll be happy to help in any way that I can.
Best regards,
Derek