It’s coming up on Christmastime, and the Chipmunks are eager for the big day to arrive. David Seville books studio time for them to record a Christmas song, while Alvin, Simon and Theodore go window-shopping. Alvin has with him his prized possession: The Golden Echo Harmonica. While carrying it around, he notices a mother and daughter looking at one on display. The girl eagerly wishes to get it for her little brother Tommy, who is very sick…