Fearthiss, I am willing to bet that you will be able to escape the Cold weather of Northern Indiana. In December, even though we were wearing winter coats at MVMCP with temps falling to the upper 30's, the next day at MGM we were back in shorts with gorgeous 75 degree sunny weather! Most of the trip we didn't need winter coats, but light jackets were useful for mornings/evenings. We even were able to get in some swim time for the kids!
Early December is a great time with the light crowds, mild weather, and the beautiful Christmas decorations. However, the one thing I don't like is that in parts of the parks, they play Christmas music instead of the Disney themepark music. I can hear Christmas music while shopping at the mall later, when I'm in the Magic Kingdom (other than for MVMCP), I want to hear the traditional Disney music!