Hi, Crystal! Several of the Walt Disney World Resorts have undergone enhancements in the past couple of years to add a pull-down Murphy bed to many rooms' sleeping accommodations. These beds are slightly smaller than a traditional twin-size bed, measure around 66" in length, and are built into the storage area of the room. My younger daughter was so excited that we were able to stay in a room outfitted with one of these beds last Christmas. As soon as she entered the room, she declared it her "tiny princess bed" and refused to allow the rest of us, her loyal subjects, to even sit on it! You can currently find these beds in two of the Moderate Resorts: Disney's Caribbean Beach Resort and Disney's Port Orleans Resort - Riverside. Some of the Disney Vacation Club Villas have also been enhanced with these beds recently: Disney Polynesian Villas & Bungalows, The Villas at Disney's Wilderness Lodge and The Villas at Disney's Grand Floridian Resort & Spa.
I just called and spoke with staff at Disney's Port Orleans Resort - Riverside about the bed rails that are provided by the Resort hotels. The lovely Cast Member even had a member of Mousekeeping attempt to use a set of the bed rails on the Murphy bed while we were on the phone. I am so sorry to tell you that the bed rails that they provide will not fit the small Murphy beds in those rooms. However, there is no need for you to worry about packing a Pack 'n Play for your little one to use during your stay, as there is a great supply of them at each of the Resort hotels. There is also a limited supply of small-size cribs that you could reserve.
Check out this recent answer to another Guest about reserving a crib or Pack 'n Play before your trip.
I hope you have a magical day, Crystal. Please let me know if you have any further questions.
Brandy