Hi Harry and welcome to the Disney Parks Moms Panel.
My family have visited the Walt Disney World Resort several times during the month of December over the years and I can tell you that the weather can vary considerably at this time of year.
Some years we've been wearing jeans, jumpers and coats to the parks whilst other years, we've been wearing shorts and t-shirts.
The good news is that although none of the Disney Resort hotels have indoor pools, all of the outdoor pools are heated to a lovely 82 degrees, all year long. So no matter what the weather is like, you should be able to enjoy the pools during your stay.
Wishing you a magical trip filled with memories which will last a lifetime!
Emma