Curtis says "We usually try to cut them (the children) a little slack around this time of year". Actually, Christmas is around the time when most children start to behave better, so it would actually be when it's nowhere near Christmas that they cut the children more slack.
Scott's family is supposed to live in Michigan, yet the sign on the front of Charlie's school reads "Secondary School". They're called high schools in the U.S. and secondary schools in countries such as Canada, where the movie was filmed.
At the end of the movie when Santa is stopped above the house, Comet is not seen on the back of the sled. After Lucy waves to Santa, she says goodbye to comet and he has appeared on the back of the sled. Actually Comet's antlers are visible in the back of the sleigh, they're just hard to see against the night's sky.