Factual error: When hero boy and girl and Billy are on the runaway car at the north pole, they crash into the stopper at the end of the tracks. They are flung backwards when in reality, due to inertia, they should have been flung forward into the guard rail.
Character mistake: Towards the end of the movie when Tim Allen is on the roof and the fire squad is called. One of the firemen carrying the ladder accidentally hits a man in the head with it.
Continuity mistake: Near the end, Mike is hanging the glass angel he got from Artie on the tree. Nina comes in through the front door, leaving the door chain hanging (unlatched), yet, in the very next shot the chain is on.
Other mistake: When James Gandolfini hits Ben Affleck over the head with the shovel for burning something in his front yard, he falls, but his head never hits the ground. You can actually see Ben Affleck holding his head up a few inches off the ground. An impossible feat for someone who is supposed to be unconscious.