Assuming turkey, you take out and let it rest well wrapped for 40 minutes or more before serving. This gives you oven space to finish off the veg - giant tray of roasties, other veg you can cook in shifts then bung in the oven - things like braised red cabbage or glazed carrots do really well for having a second cook in the oven. Sprouts you can do in two pans (or multiple steamer layers) at the last minute, or else again do something like fry them with bacon or chestnuts.
Table - pasting table extension or board joining 2 smaller tables or whatever, all covered with layers of mismatched tablecloths, and garden benches and bedside stools pressed into service for seating.
As the oldest child I hated having to have a children’s table and being responsible for younger siblings and cousins as the grownups got gently tiddled in peace. So one big squashy table always gets my vote. Just make sure the people you pen into the corner are either the adults who are least likely to need the loo mid course or else the wriggliest children who can squirm out under the table and between the legs of whoever is sitting on the more accessible side.
My own recommendation is that you gather a bossy aunt to sort out the seating - she’ll be annoying, especially if she uses her primary school teacher voice, but she’ll be right and it’ll save you the hassle!
Make sure the gravy is piping hot, and have more pigs in blankets than you can possibly think of needing, and that’ll hide a multitude of imperfections.
Kids table can be great if all children are a similar age, independent, and know each other well. But otherwise half the children will end up squashed onto the adult laps anyway, or else one female adult relative will end up exiled from the adult table in order to police it. No fun for her.
One year we did a separate Ancients table! Grandparents and Great Aunts had the best silverware and finest bone China and everyone else mucked in with the children. Meant that Elderly Relative who really couldn’t bear to watch babies learning to feed themselves got to sit facing away from the horrors whilst indulgent Elderly Relative could look on and coo without risking gravy being smeared all over their cream cashmere top.
Still prefer the giant table really though if you can do it.
Good housekeeping and Mary Berry and probably loads of others have tips about what you can cook or parcook in advance and that definitely helps. Much easier to have everything preassembled and nearly ready then need 20 minutes in a hot oven to finish off, that kind of thing. And don’t bother trying to reduce your own chicken wing stock for the perfect gravy; life is too short!
Oh - and if anyone coming is adamant that Christmas won’t be Christmas without X dish, and that’s a dish you have no interest in cooking, tell them they are welcome to bring it with them in a microwaveable dish.