Hiya Priscila! Welcome to planDisney!
Oh boy! I'm so excited to hEAR you will be visiting Walt Disney World for the first time in just a few weeks! There is nothing like your first visit, especially walking into the
Magic Kingdom and heading down Main Street, U.S.A. for your first glimpse of Cinderella Castle. It's a memory that I will not ever forget!
While each Disney Resorts Hotel has a gift shop or small store onsite, I did confirm with a Cast Member that pre-paid sim cards are not sold at these locations. However, there is a gas station on Walt Disney World property that does sell pre-paid sim cards from AT&T. I can't confirm that they will have them in stock upon your arrival, but this will be your best bet to purchase one. The gas station is located near the entrance to
Disney's Hollywood Studios on Buena Vista Drive. I suggest taking a ride-share service to get there from your resort unless you have access to a vehicle upon arrival.
My first visit to Walt Disney World as an adult also consisted of a stay at
Disney's All-Star Movies Resort. I was blown away by the attention to detail and the impeccable theming throughout. Bus Transportation to and from the parks was very efficient and we had the best time waiting to see if we got a special character bus to take us there. The resort has plenty of amenities and recreation activities to keep you busy, including multiple pool areas and an arcade.
Priscila, being that this is your first visit, make sure to stop by the front desk of your resort to pick up a 1st Visit button to wear at the parks. You'll end up having some great interactions with Cast Members and other Guests during your stay!
Have a magical day! See ya real soon!
Greg