Check out the Colbert Report first...
This is the best way to figure out if you'll be offended or not. Even though my family's Christian (this was actually one of our Christmas gifts) I enjoyed it even though it is a little long. However, Christmas's flaws are pointed out, which isn't surprising given Colbert is known for his satire and was raised in a Catholic family where he was also taught intellectualism. While this is a Christmas special, it's definitely not one for the little kids. There is a slight bit of violence from Keith's song about the War on Christmas (though kids have probably seen worse when they watch the real news about really violent wars). Also, purposely cheesy fighting with a bear and a couple of gun shots. Sex is fairly mild with the worst being the innuendo in Legend's song about "nutmeg" (right). There is also a recurring joke about kissing people under the mistletoe, and eventually kissing a (very) fake bear. Language is typical of what you'd expect of Colbert and company, mostly mild, but one moment of a lot of bleeps. Obviously, this special would promote the Colbert Report, and guests' products including the Daily Show and the music of Keith, Legend, Nelson, Feist, and Costello. There are also a couple of names dropped as mentioned in the CSM review. Drugs are limited to Nelson's song with giving pot to baby Jesus (and indulging himself), but there are consequences (he is arrested by tiny policemen... long story) and Colbert drinking eggnog with rum. Overall, Christian faith gets some good-natured ribbing ("who'd thought the wise men would look so white?"), nothing mean-spirited, which makes the special fun for open-minded teens and up.
What other families should know
Too much violence
Too much sex
Too much swearing
Too much consumerism
Too much drinking/drugs/smoking