Continuity mistake: When the Pevensies enter Narnia, Lucy is seen in several shots with her arms at her side while Peter and Susan are apologizing to her, then her arms are suddenly behind her back to throw a snowball at Peter. She was never seen bending down to collect the snowball and Peter and Susan were surprised when she threw it at him.
Suggested correction: Right before she throws the snowball, she is seen walking up to them, so presumably, she made the snowball off-camera.
Continuity mistake: When Lucy first comes out of the wardrobe, it is snowing, and some small amounts of snow are on her hair, but, in other shots, there is either less or more. It keeps switching.
Continuity mistake: When Santa puts his bag of gifts down on the ground, we see that there is a teddy bear and a quiver of arrows, among other gifts, in the bag. In the next shot of Santa reaching into the bag, the bear and the quiver are now next to each other when there were many inches apart in the prior shot. (01:09:30)
Continuity mistake: There are 3 candles on the Beavers' tables during their conversation with Peter, Susan and Lucy. The middle one becomes significantly taller when Susan tells Peter that their mother sent them away from London to escape war. (00:49:45)
Revealing mistake: During the final battle a harness is shown on the water buffalo soldier as the main centaur attacks and kills him (the harness is visible as the soldier is hoisted into the air).
Factual error: The locomotive Bradley Manor has a British Railways number plate on its smokebox door - at least 8 years before Nationalisation. GWR locomotives had their numbers painted on the buffer beam.
Continuity mistake: When being chased by the witch (which turns out to be Santa Claus) across the plain, the shadows change direction between shots, and in the close-ups there is more than one shadow per person.
