Are you looking for ideas for Christmas Day itself, or the entire season?
Firstly, think yourself, and then ask DH and DCs what they actually LIKE about Christmas (and especially anything they LOVE), particularly things that you, as a nuclear family, do together. Things you want to do, places you want to go, foods you want to eat, etc.
Are you very busy with school and work things in the run up?
Could you allow some things that normally take time in the run up to hang over until the school holidays instead? Baking, crafting, etc? Or downtime to watch a movie together?
Take time over the 30+ hours from closing the front door on Christmas Eve to the end of Christmas Day to slow down completely as your own little family unit.
Are there Carol services or similar on locally?
Do you go to Mass or Service on Christmas Day? If you don't, is it something you would like to start? Midnight services (anytime after dark here, but I know it is actually midnight in some places) can be quite magical, especially for any younger DCs allowed to stay up for them.
Or is there a gathering in a local pub or similar, or gathering of friends that you can't usually get to because of seeing family?
Could you organize your own gathering for local friends, for a couple of hours on the weekend of 21st, or even on 24th itself?
Taking time, as a family, to lay out the Christmas stockings and the snack for Santa.
Making time, as a family, to remind yourselves of the bad and good things that have happened during the year, and to think about your hopes for the coming year (we tend to do this after dinner on Christmas Eve, while lighting the Christmas Candle and just before setting out the stocking).
And take a gentle approach to Christmas Day - we tend to have a nice breakfast after the stockings, go to mass, make 1 call to a DAunt, (and sometimes a walk on the local pier), and cook the dinner in stages in the afternoon while enjoying a few M&S nibbles and some bubbles, and opening presents in between occasional forays into the kitchen. It also means there is time for DC to play once the presents are opened, and before a late afternoon dinner. We often watch something on tv later, before a relatively early night (we have DD's birthday next day to organize). And then we are not up too late feeling bloated either.
Over the holidays, we make sure to get out for a decent walk as a family (proper hike in the hills if we can, otherwise stroll through the local hilly park).
We are not a big shopping family, so we do make an effort to get to the sales one day for anything we need that may not have got as a present.
We like to build in time for a few family board games, and there is usually 1 large jigsaw being made on the table for the season (difficult ones - that people wander in and spend 5 minutes on alone, or ends up a few people spending time on it together, but they are not ones that can be done quickly). And some time for everyone to relax and do their own thing too - reading, watching tv, playing with friends from the street, etc.
And we also enjoy spending some time doing a few family meals together - both cooking and eating them together. One night usually ends up being a curry feast, with 2/3 different curries, pilau rice, puppodums or proper naan breads, etc. There are a couple of seasonal specials we like to make, like a blue cheese and ham gratin, that take time (which we don't usually have). And DD likes to do some baking, sometimes involving me and sometimes not now that she's older (12).
It's also a chance to get the house a bit organized after a busy autumn season.
But we usually go out to at least 1 movie as a family, and sometimes find a couple of other things to do too.
And catch up with neighbours - just having time for a cup of coffee and mince pie in the middle of the day is lovely.