What dates in December? If you are there before Xmas you should have no problems, If you mean Xmas -New year Mega busy, We will be there thru the busy period for the 4th time I am already dreading the crowds again but its worth it.
Only day we have seen parks close to general admission is NYE but we dont park hop so may have closed other days without us knowing.
I have highlighted in red weeks you will be there.
Info courtesy of Intercot:-
MOST CROWDED TIME OF THE YEAR
Christmas through New Year's
EXTREMELY CROWDED
Easter Week (Before and After)
REALLY CROWDED
Fourth of July Week
CROWDED
Spring Break (first week of March until mid April)
Memorial Day Weekend
Summer Break (second week of June until second week of August)
President's Day until the end of February
A GOOD TIME TO GO
End of April
Second Week of February
Labor Day Weekend
First two weeks of December
THE NEXT BEST TIME TO VISIT
First Week of February
Beginning of October until Thanksgiving
Week before Christmas
BEST TIME TO VISIT
January
September