At that age, for the break from nursery, could you establish new routines? Like them helping organise dinner every day - getting out the potatoes from cupboard, pots from cupboards, mixing things etc.
And getting them to make their beds every day - a parent with them helping, (and younger will need more hands on help than older), or pairing socks as you fold laundry etc. Just getting them involved in everyday life.
Have a baking day 1 day - but get other parent to corral them for 20 minutes beforehand so you can get organised (packets out that you need to get, things measured that they can't help with. IF you have space, time, energy and ingredients/utensils, maybe split the mixing between 2 bowls for each to do a half-batch? Do an easy recipe for this day and be prepared for interest to wane before you are finished.
And leave decorating the results to the next day - spread out the activities and your energies (and the extent of the mess on any 1 occasion!). For decorating, maybe have the icing already made, or make a couple of colours beforehand but let them each make some white or 1 colour each....and again have your bits out before letting them lose.
Some free printables from the internet (DLTK, Activity Village, Crayola and other websites) can be useful as a standby. I especially like AV (although lots are now behind a paywall) and DLTK as there are not just colouring pictures at different levels of complexity, but activity sheets which are seasonal but work on literacy/numeracy/making shapes/starting writing/word searches/,..... going right up to story starters suitable for the top end of primary school. So it's something you can keep doing just updating for their development as the years go on.
Fresh air daily, even if its raining. Walking in rain can be lots of fun, put on wet gear, leave clean dry clothes ready before going out, and the makings of a hot drink/snack. If very wet, let them have the fun of a middle-of-the-day bath and relax in that (after coming home). But different animals seem to come out when it's wet, and there are lots of different sounds, and you can see what parts of the ground are wet but how trees and branches keep other parts dry, or the side of the tree that's wet showing the wind direction.....
Other crafty projects could include potato stamping or hand printing brown paper to make wrapping paper for their presents to each other and Mammy and Daddy. Or a card for DGPs etc.
On Christmas Eve, definitely enjoy the excitement in the morning, but try to dial it down from mid-afternoon. Maybe look at tracking santa if you want, but quieter activities, and maybe a nice storytime together or watching a movie....rather than dancing around and building hyperness. Once dinner is over, definitely quieter activities - we do a hamper (I know, hated by many here) with pJs, bath bomb and hot choc that comes out after dinner, DD sets out her stocking and goes for a warm bath, new PJs and then we have a calm hot choc together before I read her a bedtime story tucked up in bed (well, that last part finished 2 Christmases ago as she's now a teen but the rest still happens). So there is a better chance she will settle to sleep well, rather than being up half the night. and thus a better chance of an enjoyable day next day. (We couldn't do it 1 year when travelling to family, they got ALL the DCs all riled up all evening, DD slept dreadfully and was in foul form on 25th because she was too tired).
Apart from whatever toys Santa wants to bring, a good idea might be a new board game that they will enjoy for whatever point of the day you can enjoy family time, or need a 1 parent cooking/1 parent occupying DCs time. It might be something that got lost behind the tree and is only seen after dinner, if that suits timewise. Or get out some favourite game to play together.
But you might also find that the new toys are a great hit, especially if a parent gets down on the floor to explore it initially and help the play get started, but can pull back, and let them at it once they figure it out or grab old dollies to meet new dollie or imagination starts to fire up...
(It might help to clear away wrappings - whether you can persuade them to help when you pull out a big bag from beside the chair, or do it around them as they are engrossed - but reduces clutter and helps reduce the aaaaggggghhhhh of a chaotic morning).
And it should be a nice day for them too for food - so if they won't eat a roast dinner, or will eat parts but not roast potatoes say, have something they will eat or a small serving of mash, or their favourite carrot sticks to munch on ...as long as they eat sufficiently. (Buffet may not work for 25th, but we do 1 on 24th every year, some things DD didn't like but always plenty she did, and she could try new things that way as SHE picked it not it being forced on her plate....and we could enjoy some of our favourite treats too even if she didn't like them).