Continuity mistake: When the they first show the Evil Snow-Plough Man, he's chasing kids and they run off to the left side of the road as proven when the kid's sled gets crushed. However, once he's past, they all pop up from a mound of snow on the right side of the road.
Continuity mistake: When the wife gets hit with the snowball thrown by her kid, she throws her phone. If you look in the background right after that you can see the phone in plain sight laying in the snow between her and the house. A fer scenes later however it has jumped to under the tree.
Other mistake: When the children first hit the principal with a snowball, the steak he is cooking lands onto a lawnchair. A few seconds later, his dog picks it off from the ground, and not from the chair.
Factual error: When Snow Plough Man drives his truck around clearing snow, he honks the horn of his truck by pushing the button on the steering wheel. The sound that is made is an air horn. In reality the button on the steering wheel of a truck honks an electric horn like a car. The air horn is actuated by a rope or cable hanging from the ceiling.