Hi Monaliza,
What a magical time of the year to be heading to the Walt Disney World Resorts! The holiday magic will be in full swing for you to enjoy.
I recommend buying a three day Magic Your Way
ticket without options. This will allow you to spend one day at a park and just enjoy that park. It also saves you travel time as you are not moving to another park. If you purchase your tickets ahead of time, they will be ready for you upon arrival at will call at a theme park ticket window. You can also have them sent to you at home so you can go right to a park. It is also a way to spread the payment of vacation. However, you can always pick up tickets upon check-in at a Walt Disney World Resort.
As for theme parks, I would vote for either two days in Magic Kingdom and one day in Epcot or one day at each Magic Kingdom, Epcot and Disney's Hollywood Studios. This would take advantage of most the holiday offerings each park has to offer.
You can ask your older children where they would like to go so that they feel like they are part of the planning. This can help narrow down your park choices.
Wishing you a magical vacation!
Beth