Continuity mistake: When the puppies are watching the television, you can see that they are watching Homeward Bound. The three animals are standing on the hill, about to head home. A few minutes later, when the nanny comes inside, we see the TV again and Shadow is with Peter. This happens at least 10 minutes after the animals are on the hill.
Other mistake: In the scene where the two robbers are following the puppy trails through the woods and are nearing exhaustion they spot the police convoy coming along the road. The cars appear to be mostly Range Rovers. In a latter scene though, Cruella joins them in the prison van and the convoy of police cars is seen to be leaving the village, but most of the police cars appear to have changed to Land Rover Discovery's, instead of the earlier Range Rovers.