If your child watches Disney Jr and knows the characters, then this show would be fun for him. Everyone sits on the floor, parents and kids, and there are live actors on stage. It is geared to the pre-school crowd and they have the kids doing things like dancing and jumping around. It is kind of fun.
The Dollar store is a good place to get the Glow in the Dark toys. Kids really like to play with them at night in the parks.
You'll have to watch the weather forecasts but most likely it will be too cold for Kali unless there is a really hot spell. If you're sitting in the wrong seat you can get totally immersed in water from the waist down on that ride.
I've managed to stay dry on Splash with just a hooded rain jacket, one of those thin, lightweight ones that are popular now.
If the safari keeps its closing time of 6pm when we are there, then the last fp for it will be at 5pm.
There are a lot of good places to watch Illuminations. We like to watch near France, to the right of the kiosk that sell the frozen drinks.
Illuminations fp is a tier 1. Maybe you can get it as a 4th fp, though.
The best children's playground at Dsiney is at Fort Wilderness. You can take the boat from CR to FW and the playground is very close to the boat dock. Then you can take a short walk to see the ponies in the corral that is right behind Pioneer Hall. There is also a horse stable back there so you can look at the bigger horses. From there you could take the jogging trail to Wilderness Lodge if you feel like taking a 22 minute walk. The path is paved. Or you can get back on the boat and go to WL that way.
The lobby of the WL has a nice little bridge that little kids love to run back and forth over. This bridge is made for toddlers.
The Mercantile is one of the most interesting gift shops of all the resorts. And the lobby is nicely decorated for Christmas.