Ah, love. You’ve built this up a lot for yourself and it’s not living up to what you hoped it would do for you.
In your shoes, I’d take it bite sized. Bake some Christmas decorations or bits for a gingerbread house, and embrace the chaos of over-decorated bits of biscuit. Another time, go to a local shopping centre or somewhere with a tree or markets and let the kids stare at the shinies.
One thing we’ve started this year is we’ve brought down all the Christmas-themed books to a special shelf in the living room so that when anyone wants a story we’ve got a Christmas one to hand. The 3yo in particular is loving it but the 7yo is really enjoying snuggling up to listen. Stuff like Stick Man, the new Pip and Posy book, the Jolly Christmas Postman, Mog’s Christmas, Slinky Malinki’s Christmas Crackers etc. I can’t believe we’ve only just done this. It’s so lovely curling up with my (big)!babies for a story after a hellish day at work.
Where in London are you? I might have specific ideas for easy spur of the moment things.
I think the most important thing, though, is to try not to expect any of these activities to make a magic difference. They probably won’t, but they might help with the guilt you’re feeling for your kids (which probably they are feeling very Christmassy anyway).