Fuzzpig, it is usually only DH, DD (6) and I for Christmas in our house. We do some visits to family locally (wider family as both our immediate families live 160 miles away) early in the day, but once we are home, it is just us.
If we didn't have to do those visits, it would be even more relaxed. Santa in the morning, with a nice early walk followed by big brekkie (full fry or bacon sarnies with buck's fizz would be ideal), pottering around making the dinner (I don't tend to over-do that anymore), fire lit, nice nibbles for peckishness during the day, presents mid-afternoon from under the tree and dinner in the early evening.
If you are home all day, you can prep the dinner on the day entirely (especially if you plan to start eating between 4-6 say). But you can have lots of the "heavy lifting" done in advance. Depending on what you like - soup frozen, potatoes for roasties can be parboiled and frozen, sprouts can be blanched and frozen, cake and pudding done (or bought) well in advance...But as I am not great on having freezer space or remembering those sorts of things, I tend to peel potatoes and veggies the day before - potatoes in a pot of cold water overnight, veggies in other pots of water or airtight containers (depending on which suits better - carrots best in water, sprouts either, courgette, cauliflower, mushrooms, garlic, onion etc all best no water). Dh makes the stuffing the day before too, and if I am bothered, I boil up the turkey neck and giblets with the carrot and onion peelings to make a cheat's stock for the gravy.
There really is no point in stressing as then you don't enjoy it and kids may pick up on that too. But it's really just a bigger Sunday roast than normal - and if you don't want that kind of dinner, that's fine. Go for something that suits YOUR family's tastes and your pocket better.
Having a few board games to pull out too can be handy - it tends to say that it's a different day when we do that here!! (They come out either on hols or Christmas here mostly for family play - it's usually DD's friends playing them other times with her).