When the Great Ak and Young Claus travel the world, they're supposed to be invisible, but blurry so that the audience can see them. When they reach their last stop, which shows two armored men fighting, the Great Ak and Young Claus are fully visible.
The first two times Claus walks through the village to deliver the gifts, the valley looks like it's summer time, when in fact the movie takes place in a snowy village called The Laughing Valley.
The children sing about Claus' toy cats with "yellow-green eyes," yet the eyes are wholly green.