Revealing mistake: When the kids step out of the water and walk towards the house, the floor is already soaking wet from previous takes.
Continuity mistake: When the Leslie Special is rolled out to be presented to the Great Leslie the red carpet in the front view starts at the building alignment. The aerial shot as seen from Professor Fate shows a wide gap between the building alignment and the red carpet.
Continuity mistake: After Father Frost meets Nastenka, he gives her his cloak for being so graceful towards him. Between wideshots ans closeups the position of the cloak on Nastenka repeatedly keeps on changing. (00:50:55)
Continuity mistake: Charlie Brown's Christmas tree is never the same. When we first see it, it has three branches. Later, when he's carrying it, it has four branches. Then, when he tries to decorate it and it flops over, it has six branches.