OK, I am going to try and adapt my thoughts for a baby and toddler.
We always bake on Christmas Eve - cookies for Santa. We do more elaborate baking other times in December but on Christmas Eve it's a simple recipe that rolls and slices. And I always have a batch done earlier in December so I freeze half the batch, to slice and bake from freezer if things are not going well on the day.
That might be asking too much this late on, but you could get the ingredients out tonight and pre-weigh them so it is easier to supervise the toddler tomorrow. Also, because it works better to bake after a period in the fridge, you can do the mixing and roll into a sausage to put in the fridge as 1 slot of time, and then slice/place on baking tray/put in oven as a separate slot of time, and then the quality control testing (once cooled) with a glass of milk or similar is another slot of time spread throughout the day.
Carpet picnic to watch a favourite cartoon, seasonal movie, something on tv, with a snack and a juicebox could be fun too.
Do you have any Christmassy stories to read together?
If you have a printer, you could print some colouring pages from various websites (Santa update certainly used to have these, and places like DLTK, but I am not sure which currently have free printables but a google search should find them for you). Or organise yourself tonight when they are in bed to put a craft kit together for tomorrow - say a couple of paper plates, string and red and black crayons to make a Santa mask, or some plain paper and kid friendly scissors to make snowflakes or a string of paper angels to hang in the window....it's a "kit" because you have grabbed all the bits and pieces you want for a Christmas craft all together in 1 place, so tomorrow is about taking out 1 bag and getting toddler involved to do it, without having to pull things from 6/7 different places before you get started and toddler finds a favourite toy or wants to do something else they've seen etc.
Also, some fresh air is great. A walk in a local wooded area to see what the birds and animals are doing to get ready, how the trees look different in winter and birds are grabbing berries to eat....or along the seafront and splashing in the tiny waves (wear wellies, waterproof trousers if you have them, and bring a change of clothes in the car as well as a snack for after the exertion)...or somewhere local that is doing something special for Christmas Eve etc. Gets you all out of the house and also wears out DCs a bit more for a nap in the afternoon or an early night.
I started this at lunchtime and got called away with work, so there are probably loads of great ideas by now. Enjoy!