Hi Krista,
Happy upcoming birthday to the twins! Five years old is a big deal and how wonderful that you're planning to celebrate in Walt Disney World.
Typically, you can celebrate at a restaurant or in a private room. Of course, the private facility route is more expensive. For a private room, you'll need to contact Disney’s Catered Events (321-939-7278).
Here's a link to lots of
celebration ideas.
If you went the restaurant route, I would pick a fun location or a place with food that the twins love and make an Advance Dining Reservation for the entire group. Then, go ahead and order a birthday cake.
Another fun place to hold a party would be at Goofy's Candy Company in Downtown Disney. They have a space for parties there! Call 407-WDW-BDAY or
407-939-2329 to inquire or book your party. Once upon a time, birthday parties were possible at the Neverland Club at the Polynesian Resort, Disney's Winter Summerland miniature golf course, and Blizzard Beach water park. I'm not certain if these are still options however the birthday hotline number would be able to give you up-to-date information.
Or consider a private
fireworks cruise on Seven Seas Lagoon. You can have the pontoon boat decorated with a birthday banner!
There's a whole "world" of possibilities. Let me know if I can help any further.