Grandma Got Run Over by a Reindeer (2000)

As if young Jake Spankenheimer doesn't have enough problems on Christmas Eve, he has to help his mom and dad prevent mean-spirited cousin Mel from taking ownership of the family store. When his grandmother gets lost in the cold in the midst of the confusion, Jake is sent out to find her, only to discover that she's become the victim of a rather unusual hit-and-run accident, and that Santa is real but not quite the sort of guy he was expecting.