Hi Katie,
Thanks for stopping by the Disney Parks Moms Panel with your question. What an incredible event to celebrate! You must be counting down the days to having your children's adoptions finalized (I'm sure they are as well).
Katie, Disney does not normally post when their decorations will flip from Fall to Christmas decor. However, I can use a little bit of information that's already available to make an educated guess. The Walt Disney World Resort always ensures that the Magic Kingdom is decorated for Fall through the last
Mickey's Not-So-Scary Halloween Party; this year, the final party is being held on November 1, 2019. I would hazard a guess that it would only be a day or two after that last party that the park will be transformed for Christmas. The change would certainly occur prior to the start of
Mickey's Very Merry Christmas Party (dates have yet to be announced as of this writing, but keep checking the link for updates).
As for the other parks in the Walt Disney World Resort, I would also guess that they would have a similar decor schedule as the Magic Kingdom (give or take a day). If you are arriving in mid-November, I would guess that you will have decor in each park that is worthy of the most incredible holiday cards you've ever sent! Don't forget to take advantage of the
PhotoPass photographers in each park to ensure that each member of your new family is included in every precious photo.
Katie, congratulations on your new additions!
Best Wishes,
Amy S.