Continuity mistake: When Mary and Laura dive into the lake to rescue the puppies they have their shoes on. As they are swimming around looking for them they are barefoot. When the get out of the water their shoes are back on.
Continuity mistake: When Jason and Laura are flying the kite in one scene, there is heavy rain, thunder, and lightning and dark storm clouds shown in the sky, but on the ground showing the kids, the sun is shining on them (note the shadows).
Continuity mistake: In the scene showing the kids on the caboose as Charles tries talking to them from the train, the sun is on one side of the kids; then, a short time later in the same scene, it's on the opposite side of the kids (the caboose never made any turns in this scene).
