Welcome to the
Disney Parks Moms Panel, Jennifer! We appreciate you have reached out with your question!
You should not have a problem at all bringing a cake from outside! Guests are allowed to bring in a cake from outside property at any time. What I would do, though, is notify the Cast Member assisting you at the podium when you register, just so that your server knows you might need some extra utensils (a knife and a shovel) to cut the cake.
Remember that you could also order a cake within Walt Disney World by calling (407) 939-3463 and that way you will save time and will not have to carry the cake around with you; instead, it will be waiting for you at the restaurant of your choice (*see all
details and participating restaurants in this link)! I strongly recommend you add one at the time of booking your meal. If not, you can still add one to your
dining reservation later or ask Concierge at your
Disney Hotel lobby ahead of time to help you out with this.
Jennifer, please come back with more questions about your vacation at
Walt Disney World Resort. We'll be hEAR waiting for more questions!
See ya real soon,
~Desiree