I agree with all that has been said, but am adding the following:

Rockefeller Center area: - two blocks from the Crowne Plaza, Times Square

Stop into St Patrick's Cathedral, across the street from  Rockefeller   Center. It is  gorgeous, especially at Christmas. Saks is right there  and usually has good holiday windows.  All the department store windows are fun to look at,  Lord and Taylor and Saks are usually  traditional, Barneys (Madison and 61st)  sometimes gets  politcical or just plain funny. One year they showed  gifts that  each of  the Sex and the City might receive. .. Let yourr imagination  run wild and you will figure out some of the gifts.  .

Rockefeller Center skating is more expensive than Bryant Park or Central Park, but  has the most holiday excitiement.  And there will be a Santa (sometimes with sled) skating along side of you. The restaurants dfacing the skating rink need reservations  and you might have a hard time getting a table near the window.

Teenagers also like the NBC tour,  touristy, but isn't that what you are.

Pass by at night to see the tree.  It is magical. Walking along 5th Ave is also  wonderful at night.   Notice the Cartier building;  It's lights go  all the way to the top, replicating a  gift box, complete with bow. Everything  else is lit up, too. .  Notice the star hanging in the air at  5th and 57 and the Channuka (sp) menorah ,  adding a  light for 8 days.   Look south  to the Empire state building ( 5th and 34th)  which has lights, appropriate for holidays, so it will be red and green shining on top.

Shopping

  Bloomingdales and Macy's offer discounts (11% ?) to out of towners.  Go to the Visitors Center for the pass, which is good for the day.  If you return, you need to get another pass.

Museums

Teenagers like the  Museum of Natural History, and the Plantarium next door to it (Central Park West and 79th). Two minutes away is the NY Historical Society, a small easy to navigate, museum featuring a " Lincoln in New York exhibit.  You can have a nice lunch around the corner at Isabellas on Columbus Ave.

  Pick up a copy of Time Out or New York Magazine which will give you a good rundown  of what's what  and where, during the week you are in town.   The Times is especially good on Friday. If you have specific interests, let me know.  I might be able to make suggestions..  But the city is so wonderful around Christmas. You will  walk everywhere and have a grand time.  And let me be the first to say, "Merry Christmas"  It will be.   You 'll see. .