We normally go to Disney in December, we've been around 10 times now. We have gotten all different kinds of weather. We have had weeks where it was in the 80s and only got down to the upper 60s at night and we have had weeks where it didn't get above 60 some days and it was in the 40s at night (cold when you are outside for hours at a theme park).
My best advice is to watch the weather before your trip and pack from there. The weather will at least tell you if you should pack heavier on winter or summer clothing. I would bring a little bit of everything though despite what the weather says. I would bring warm jackets for everyone and hats and mittens. If your daughter is still using a stroller bring a lightweight fleece blanket for waiting for nighttime entertainment.
My typical December packing list is the following:
2 pairs of pants (in addition to the pair I wear on the plane)-wear in the parks at night.
2 pairs of capris-for park day wear
2 pairs of shorts-for park day wear
5 tee shirts-one for everyday in the park
3 long sleeve tees- to wear over my tee shirt in the morning while its chilly
2 sweatshirts-for evenings
1 medium weight jacket- to wear on cold evenings (this would be my 30 to 50 degree jacket, normally a soft shell northface)
Winter Hat
Winter Gloves
Scarf
We normally go for 5 nights with 4 park days. If it looks like its going to be a warm week I bring my swim suit because the pools are heated

I bring sandals but normally just wear sneakers in the parks, my feet get cold!