While my family has stayed in the cabins and loves them, I think by looking at your post, this place will be a little overwhelming to you without any help for your toddler. You may feel a little isolated, especially without the help of a golf cart. We stayed at the cabins, Pop Century, and French Quarter in June. My 3 year old grandson loved them all, especially the bunk beds in the cabins. However, I think the Pop Century was especially fun for him because of the water jet play area and baby pool. He loved the slide at the POFQ, but in December it may be a bit cool for the pool. If it were me and I was traveling alone with my grandson, I would stay at the Pop Century or possibly one of the resorts on the monorail. We have not stayed at the deluxe resorts yet, but if you have the money for it, it may be worth a try. Moving around to the parks with a toddler can be trying at times. I don't want to sway you from your plans, but you may find that at the end of a day in the parks you still are another bus ride away from your cabin. By that I mean that once you return to FW, you must catch another bus that runs the route inside the campground to the cabin loops. The campground itself is a beautiful and relaxing place, don't get me wrong. But I think with just the two of you I would look at something a little more convenient transportation wise. There is a nice boat at the campgrounds which goes to the Magic Kingdom, but you still would have to take a bus from your cabin to the boat launch area to get there.
I hope that helps. I don't want to confuse you any further. Good luck with your planning, and have fun!