As Father Mouse and Albert enter the Trundles' house to see the model of the new clock tower, we see a clock that reads 10 o'clock in the long shot. After Father Mouse and Albert finish bouncing down in the next shot, the clock reads 11:10.
When Santa first shows up, his cheeks and nose are rosy. Then when he lands in the Trundles' hearth, the rosiness is gone. In the next shot, his cheeks and nose are rosy again.
As Father Mouse and Albert are entering the children's hospital, Albert does not appear till after Father Mouse opens the door.
Mr. Trundle's hands change position after he finishes reading the first part of "'Twas the Night Before Christmas".
As Father Mouse pushes the door open to the children's hospital, he is seen leaning partially away from the door in the long shot. In the close-up, he is seen leaning toward the door, after he's done pushing it.
Father mouse is showing his son the small clock and tells the son that when the clock hits 12, it will play a song. The clock shows it is 12 minutes to midnight. The son moves the hand of the clock to make it midnight and the song starts to play. Father mouse gets all mad and changes the hand back to 12 to midnight and says "You'll wake everyone up!" But why should he care? In 12 minutes, the clock is going to strike midnight again and the song is going to play and possibly wake everyone up anyway.