Hi Darlene,
Thanks for visiting the Disney Parks Moms Panel with your question!
Disney's All-Star Sports Resort is so much fun. Florida is known for rain showers; however, the lucky thing is that most often, the rain showers do not last all day, and December is not a particularly rainy month on average in Florida. Typically, there may be an hour or two of rain and the rest of the day will be fine. There are of course some days when it rains all day, but not too often. At Disney's All-Star Sports Resort, there is an indoor arcade called the Game Point Arcade where you son might enjoy spending some time. If it looks like it is going to rain all day, you might consider a visit to Downtown Disney to spend some time at
DisneyQuest Indoor Interactive Theme Park, which has classic arcade games, virtual worlds, and so much more.
As for Christmas Day, if you are planning to go to a theme park, I suggest that you arrive early. Christmas Day can be a very busy day at Walt Disney World, so you want to arrive early to be sure to do any attractions that you like earlier in the day with less of a wait. If this is a day that you are not planning on going to a theme park, and if you are concerned about rain on that day, a favorite activity for my family is to visit the Walt Disney World resort hotels. You can see amazing gingerbread creations and beautiful decorations at the resorts on the monorail - Disney's Polynesian Resort, Disney's Grand Floridian Resort & Spa, and Disney's Contemporary Resort. You will even be able to stay quite dry doing this!
I hope that this has given you some help in planning your vacation, Darlene. Please do not hesitate to ask if you have any further questions.