I normally have to go to work too, but even with lunch and last minute food buying (city centre M&S is actually pretty decent compared to suburban supermarkets!), we are home by 2 ish.
We always try to have a walk in the beach or to the park up the hill.
Yes, there is prep work. But done gently. Dh lights the fire. DD bakes cookies with me for Santa - I have a roll of dough in the freezer to just slice and bake, if we are tight on time, and I don't really want to do a fresh batch from scratch. Or it might be starting with eggs and butter....
Dinner is something nice, special but easy.
I try to make sure I take time to sit with dd and watch a movie in the afternoon. I have christmas radio going in the kitchen.
After dinner, the youngest lights the Christmas candle, we remember the good and bad things about the year just gone, including getting dd to remember things she thought were good and bad. We follow that with a prayer.
Then I get out the Christmas Eve box. It has DDs stocking, new pjs for everyone, naice hot choc mix/blocks of choc to melt, a Christmas beer for dh, our family copy of "Twas the night before christmas" and bath bombs for dd and I. She gets the cookies, milk and carrot in the kitchen and goes up for her bath.
So it's a mix of prep and slowing down to contemplation and relaxation.
If I was home with dd all morning, I probably would have some free printable colouring sheets from the net, to colour a picture for Santa,, and maybe some strips of coloured paper and a roll of sticky tape to make paper chains for the hall or her bedroom. To keep them busy.
And there might also be presents that she needs to wrap, to Dh or someone. And it's a day I can persuade her to help with housework , sweep the floor or help Hoover, for Santa coming tonight. Or carry clean towels down to the bathroom downstairs, or fresh loo roll in case Santa needs a wee.