Should I bring anything? And thank you for that open invitation. I promise I know how to knock and wouldn't barge in without just cause.
[Adults]
From what I can tell, it can vary so much from one family to another, not to mention country to country, city to city, branch to branch of Christianity. I think having the bare bones is a good place to start. It might be a little late, but I just recently discovered if you write a letter to Santa Claus, and you mail it, you will get a response. Someone responds to the letters. It might be a little late to actually mail them (you don't need postage), but you could arrange for them to write to him if they want, and you could find someone to write a reply and have it delivered to them. Maybe left by the cookies and milk display.
You have a tree and lights and decorations. I don't know if it's a common tradition or not (I assume so based on what I've seen and read), but you could all go out and look at the lights and decorations in the city.
And there are a lot of Christmas movies. They have to be part of a lot of people's traditions. Maybe have a cocoa and cookies and movies night?
I don't mean to give suggestions if that's not what you're looking for. I'm just learning this Christmas thing as I go, too. Thought it couldn't hurt to share some thoughts I've had recently about how to celebrate it. Just in case they might be helpful.