It's a 'ringing in' of the Christmas Season at Disneyland, so to speak. It usually takes place the first weekend in December....and so forth and so on. Carollers and such and a celebrity narrator are all in tow.
If I am not mistaken, Dick Van Dyke was this years narrator. All of this takes place up at the Main Street Train Station - a huge stage is mounted up there and this is where the carollers 'proceed' too from Main Street.