Kyla,
That time of December is a great time to visit! Low crowd sizes paired with all that great holiday decor! You will love it!
That Saturday will be busy, simply because it is a weekend, but not really all that bad still.
Here is where I would go, assuming you have a resort rest-stop midday so your little one doesn't get too worn out;
- December 10 - Magic Kingdom (am and pm)
- December 11 - Hollywood Studios (am) / Magic Kingdom (pm)
- December 12 - Epcot (am and pm)
- December 13 - Magic Kingdom (am) / Hollywood Studios (pm)
- December 14 - Animal Kingdom (am) / Magic Kingdom (pm)
- December 15 - Epcot (am) / Magic Kingdom (pm)
A few days I have you NOT hopping, though you could still "hop" to a dinner in another park if you thought you wanted to. The key here is that you should avoid any unnecessary travel between parks, as it is wasted time that you could have had in the parks, and it can tire your little one out.
Oh, and to your question, each park has something that your little one will like, so I would hit all four.
Have a magical vacation!