The week before Christmas is typically better than the week between Christmas and New Years. When we go at that time we just pick out the things that we really want to do and concentrate on getting those done. After that we do whatever else we can fit in. If they know it will be busy and are expecting that it should not be a problem. Tell them to relax and enjoy everything around them. Christmas at Disney is wonderful!!!
We are going this year again and are planning on doing the parks before Christmas and other things outside of the parks after.
It can still be a great trip with the right frame of mind!