This will be our second time going to WDW over Christmas & New Years. With the experience we had, I will say it will be SUPER crowded, especially on Christmas and New Years Eve. We spent New Years Eve at Epcot last time and it just was not kid friendly, we were very disappointed. There was a lot of drunks and TONS of drinking which then leads to stupid adults. Anyways...
1. Dont expect to do everything, pick the few much do's and try to book FP's for those.
2. On prime days get there early, like on Christmas morning if you want to spend the day at MK, be there at rope drop, it will close due to capacity.
3. Book ADRs asap if you havent already.
4. Plan 1 park per day, like you have. We never leave the park, not for a break of anything. It just seems to waist time, I rather find a cool attraction to rest at or book our ADRs around a time I know we will be ready for a cool break.
Have fun and enjoy. I remember Main Street on Christmas last time was just NUTS, you couldnt move, total jam of people. Make sure the children all know where to meet if seperated and everyone knows who is safe to go to for help and that they know an adults cell number.