My best advice to you would be to subscribe to the unofficial guide touring plans website (google it). As a previous poster said, the parks will be EXTREMELY crowded (as in, they are so packed they actually reach capacity and close the parks).
You'll need to have a really good plan, and the Unofficial Guide website will tell you which parks to avoid on which days to maximize what you see. Another thing I would suggest is making all of your dining reservations several months prior to leaving, because the restaurants will be far too packed to just walk in and get a table.
If your dates are flexible, I would suggest you change your reservations and go a week earlier...the xmas decorations are still up, but the crowds are about 1/4 of what they are during xmas. The room rate will probably be much cheaper (you're talking going from peak season to value season, just be moving your week back), and your family will certainly be able to see and do a whole lot more. Just my two cents!
Either way, have a great time!