Continuity mistake: In the boat race scene, before the bully crushes the first boat, you can see his 'henchman' next to him, even on a close up. After the boat gets run over, the kid changes into one with a yellow shirt saying, "Hey you can't do that!" After the bully says, "I just did," he nods over the same 'henchman' that was there before, to shove the kid out of the way.
Continuity mistake: When the Littles have their first meal together, when it shows a close up of Stuart looking at the gravy bowl, his milk has completely vanished.
Audio problem: When the alley cats are chasing Stuart and he's trying to start his car, he says "Come on" but his lips don't move at all. On top of that, wherever we see the cats running or from a distance, their mouths don't move at all when they talk.