If the weather is okay and night warm, why not pitch a tent in the back yard and camp under the stars! Tell each other stories and watch the stars come out.... might be hard to see if you live in the city....
Okay, another alternative could be if you have a Christmas tree inside, why not set up camp under it for the evening and watch those lights instead!
Put on some Christmas movies or music and chill out for the night.
Who ever happens to fall asleep under the tree, can stay there!