The atheists from this board aren't interested in sharing their own beliefs, their primary function (besides getting drunk and taking their kids to the gambling and prostitution capitol of the world, it seems) is to spend time attacking Christians for THEIR beliefs.
Fortunately, Christians do not get drunk, gamble, have sex outside of marriage or disparage the beliefs of others...oh, wait.
Your original question was : "So atheists...how do you celebrate Christmas?" Your question should have been, "So, non-Christians...how do you celebrate Christmas? There are many people - including me - who do not accept Christianity, but whose belief in God is as strong as yours. If defining all those who do not believe the same way you do as "atheists," then you are an atheist as far as I am concerned.
In answer to your question, my wife and I (there are no kids in the house) celebrate the same way that most Christians traditionally do. We listen to Christmas music and watch Christmas shows on TV, such as A Dog Named Christmas, A Christmas Carol, How the Grinch Stole Christmas and anything to do with Charlie Brown and Snoopy. My wife, who is a Christian will read the Bible and watch a few television ministers, especially Charles Stanley and Joyce Meyer. I watch, too, because I like to know how others think and feel. My wife and I attend the Church of Christ. I always go with her because it makes her feel good, it does me no harm and I love acappella singing.
I have studied the Bible for over 60 years and the Qur'an for a little over ten years. I do not accept either Book to be the complete, inspired and inerrant word of God. I am convinced that God will not judge us by what we believe, but rather how we live our lives in accordance with that belief. Belief is not volitional; that is, we cannot will ourselves to believe one way or another. The idea that one can believe upon command is illogical and contrary to human nature. Rather, belief is an involuntary act; belief is our perspective created by our total life's experiences filtered through the prism of our individual preferences and prejudices. Our beliefs are the product of the fickle forces of heredity and environment, things that are more controlled by chance than choice. We are not so much masters of our beliefs as we are its slaves; therefore, I am persuaded that God would not judge us by what we believe, but rather how we act on those beliefs.
Poet Shelly said it best:
"This is the pivot upon which all religions turn; they all assume that it is in our power to believe or not to believe, whereas the mind can only believe that which it thinks true. A human being can only be supposed accountable for those actions which are influenced by his will. But belief is utterly distinct from and unconnected with volition; it is the apprehension of the agreement or disagreement of the ideas that compose any proposition. Belief is a passion or involuntary operation of the mind, and, like other passions, its intensity is precisely proportionate to the degree of excitement. Volition is essential to merit or demerit. But the Christian religion attaches the highest possible degree of merit and demerit to that which is worthy of neither, and which is totally unconnected with the peculiar faculty of the mind whose presence is essential to their being" (Notes to Queen Mab).
Oh, by the way: Merry Christmas!