I think you are going to find that the 24-105 is going to provide a good range for your trip.
I shot my trip to Disney with the 16-35mm on a 40D (24-55mm effective focal length). This allowed for the best "in the moment" photos as we were very close to the kids all the time; the wide angle provided a good opportunity to include the various venues in the background. We did have two other cameras with us, point and shoot, and got some good candid photos from them.
If you want to get closer, rent the 70-200mm f2.8 for the week. Just note that there are really not a lot of good opportunities to stand back and take a long shot at the park (without passerby interference).
Curious to know what lens you used with the 60D.
I went to WDW last year twice. I first went with the 18-200mm and that was nice. I later went with the 15-85mm usm and brought the 18-200 and only used the 18-200 for the lights action stunt show. otherwise the 15-85 covered everything. I used the 270 ex ii speedlite since it was the perfect travel flash. I would have loved to try the 17-55 but I did not own it then.
Now that I have the 5d3 I want to make my decisions that will help for the trip and all the other family shots. I just may get the 50mm 1.4 or the 28mm 2.8 coming out and rent the 70-200 f4 is for the trip and see how it does. Some of me is considering just bringing my current setup for the important pictures and getting something like the Canon sx40, g1x or sx260 for my zoom needs. This way I will not have to bring out the dslr for every shot but the money spent on that could go toward another lens. What would be a good travel companion when the dslr is just too much or you want a pic but fast and then go back to the family.