Hiya Teresa!
Welcome to planDisney! Oh, Teresa, you are going to have such a fun time and I am very excited for you! My kids are around the same age and I find it has been the perfect age to visit the Parks. They are both still little kids but they are
tall enough for most rides and can remember their time in the Parks.
I think it is a great idea to visit Magic Kingdom Park and Disney's Hollywood Studios on special event days. Many people don't like missing out on the evening fireworks displays that are normally shown to all guests on regular days but not on party days. Those evenings have a special fireworks show that is just for party guests. As a result, guests who want to make the most of their day go elsewhere. I cannot guarantee it will be an empty Park but if you start early you may find that the day may go pretty smoothly. For both
Mickey's Very Merry Christmas Party and
Disney Jollywood Nights, guests with party tickets can enter the Parks around 4 pm. I find wait time to jump a little at this time as Park guests and party guests start to overlap.
If you plan to start the day at rope drop and stay till closing (usually 6 pm on party days) or 5 pm then know that it will be tiring no matter who you are. I suggest a nice long lunch break in the middle and slower activities in the later part of the day such as shows to cool down and rest your legs.
Walt Disney's Carousel of Progress is my go-to afternoon activity. It has a very short wait time all day so I don't waste my Rope Drop morning on it and focus on more popular attractions. I then save it for the afternoon where I can savor the various scenes and hunt for hidden Mickeys.
I feel like you will not know how much energy your kids will have for a normal Park day until they do it. It is tiring and little legs have to take more steps to match one of ours so it wears them out faster. The long lunch break, afternoon shows, and plenty of snacks help. There is nothing like a midday
Dole Whip Pineapple Float to reenergize one for the day left to be enjoyed.
I hope you have a magical time with your little ones. Savor every moment and let us know if you have any more questions!
Happy Planning!
-Nimmy