Christmas is my "thing", so we have a lot of traditions. Some of my favorite are giving my girls a gift they get to open on Christmas eve, which is always the same, new PJ's they wear to bed so we have cute pictures Christmas morning. We leave out milk and cookies on Santa's special plate. I take a picture of them holding the milk and cookies in their new PJ's, and some day hope to get organized enough to put them all together!
Last year, for the first time, we made a simple gingerbread house (my girls are older than yours, 5 & 7), and it really helped them focus on something other than their excitement. They are already asking if we are going to do it again because we "always" do!
My husband reads the girls The Night Before Christmas, and of course we snap a picture. After "Santa" comes, I like to take pictures, to have before and after shots.
Most important, we make sure to talk about how lucky we all are to be together, to have each other, a warm safe place to live and food to eat. My girls like the presents, but I can't begin to express how proud I am to hear them say "we are all together and that's what's important" or something similar, and look at their face and know that they mean it.
Have a great holiday.