Advise them to make a loose schedule of which park on which day and then make ADRs accordingly. If they don't, the kids are going to get cranky when they're hungry and it's no fun trying to find a place to eat at the last minute. With at least one daily ADR (and preferrably 2), they can be assured that they will get to sitdown and eat on a regular basis.
Tell them to arrive at the parks prior to opening time. At least 30 minutes and closer to 45 minutes would be better. This is really serious advise for anyone traveling during peak times but especially during the holidays.
Encourage them to have a touring plan for each park. It helps to prevent you from criss-crossing the park repeatedly and wasting time.
Educate them on FastPass usage. They should always have at least one at all times.
Discourage them from being in the MK on Christmas. Everyone wants to be in the MK on Christmas. Everyone will be there. They can expect wall-to-wall people and tremendous wait times.
Hook them up with this link from
Touringplans.com. It can help them decide where they want to be each day of their trip.
I wish them luck. With over 10 trips to the World under my belt, Christmas and Easter are two seasons that I have avoided.
