Hi there, Lindsay, and welcome to planDisney!
I will say that you sound like one of the coolest aunts ever. Your niece is going to be so happy when she gets her special gift. I’ve personalized Mickey ear hats for family and friends throughout the years, and it is a very easy (and mostly quick) process.
As of now, you won’t be able to pre-purchase personalized Mickey ear hats through Walt Disney World. There are some third party vendors who may be able to create something beforehand, but the real magic is in having the official Mickey Mouse gear.
So, here’s my idea: Perhaps there is some way that your family can enter the parks as early as possible (without your niece so that it’s a surprise) and then meet up with her later to enjoy the rest of the day. They can visit Magic Kingdom’s
Curtain Call Collectibles, near the front of the park, EPCOT’s
Gateway Gifts, or Disney Springs’s
Wonderful World of Memories shop as soon as they open. Make sure to send your family the exact wording (up to about 16 characters/letters) and an example of the colored thread that you’d like for the Cast Member to embroider onto the ear hat. The ear hats are subject to availability and they usually take a couple of hours to embroider. They will inform your crew when the hat is ready. After they pick it up, they can surprise your niece somewhere in the Disney Parks. I’ve added a video to this answer where my friend Frances and I share Disney World birthday celebration locations and ideas.
AN EXTRA GEM: Another layer of magic would be to gift her a short, professional photo shoot with a Disney PhotoPass photographer. The
Capture Your Moment photo shoot sessions are one of my favorite ways to celebrate milestones and family memories. These in-park sessions can be reserved and paid for online, so all your family needs to do is show up to the meet-up location and have fun!
I hope that this answer helps you with the birthday surprise, Lindsay. And if you have any additional questions, feel free to
reach out to us here at planDisney. I’m all ears!
Magic always,
LeAndra