I have not been to Oz (yet) so cannot comment. With regards to christmas and New year days. I agree that it is no different now. 20 years ago, then it was quieter but not now.
If the trip is to be in Y, then it would seem best to break the journey - if only for one night. Two small children must find such a journey irksome (even if you are a FFM millionaire and everyone up the front! I understand that it is easy to break the journey at differente places out and back. Make the stop over part of the holiday.