Finishing his rounds on the morning of Christmas Day, flying over downtown Chicago, the sun is over the horizon west of Chicago, Sunrises occur in the east, not the west.
Not a mistake, but another elf sighting within the movie. In the Parent's Day scene in Charlie's classroom, watch the boy sitting directly behind Charlie in the blue shirt. When Charlie walks back to his desk to retrieve his glass ball to show everyone, you can see the boy's pointed ears. Another note of interest is when Charlie says "my Dad is Santa Claus" and it cuts to a wide shot showing all of the kids, this kid is the only one not laughing.