Hi there, Sheryl!
On October 31, the Magic Kingdom will be decorated fully for Halloween. Please be aware that
Mickey's Not-So-Scary Halloween Party will occur that night, and the Park will close early for those who do not have tickets to the event. You'll want to make note of the hours and plan accordingly.
Beyond the decorations, you won't find too much out of the (magical) ordinary that day.
A thought: Consider celebrating your little one's birthday at the Halloween Party! She'll dress up and trick-or-treat around the Park, enjoy an incredible fireworks display and special parade, and see all of her favorites in their holiday best.
In any case, how about a character dining experience on her birthday? And order a cake when you arrive, as you can do at every Disney restaurant. Try for Chef Mickey's in Disney's Contemporary Resort or 1900 Park Fare in Disney's Grand Floridian. Neither of these is in a Park, and will not require Park admission, which might work with your plans. 'Ohana in Disney's Polynesian Resort does a character breakfast, too. Just call (407) WDW-DINE or
go online to make your reservations.
And make sure you get a complimentary birthday button. You can do that at any Guest Relations window throughout the Parks or at a Resort check-in desk (i.e. if you choose to dine at one of the Resorts). You never know what pixie dust will be sprinkled on a birthday girl!
Have a wonderful time!
See you later, celebrator,
-Deborah B.