Continuity mistake: In the scene at the Rangers Station, the tuning dial on the radio disappears and then re-appears.
Continuity mistake: When Spike is fighting against the wolf on the bridge, the wolf rips off Spike's collar and sends him flying through the air. While he is in the air his collar is on and when he is holding onto the side of the bridge, it is off again.
Continuity mistake: During the part in the basement when Stu sprays the fire, we see that Drew's shirt is not ruined or burned in the background. In the next shot, when Drew walks towards his brother, his shirt appears as if it caught on fire. (01:13:19)
Continuity mistake: The rocking chair that Lou is sleeping on is facing the side away from the doorway alongside the table next to it. When the delivery guy starts walking in to pick up the box and give the receipt to Lou sleeping, the chair and table are straight next to the doorway.
Continuity mistake: When the monkey's owners are having coffee and donuts at the train station, they notice that the monkeys are on the train. When they go out going after the train, they seem to be on a sidewalk next to the railroad tracks. But then in the next shot when the train fully has ran away, boards have appeared, basically to keep the owners safe from those tracks.
Continuity mistake: When Grandpa Lou and Stu are looking through the front driveway noticing the Reptar wagon and babies are missing when seeing the bottle on the carpet, the bottle is still on the carpet with spilled milk. When they return home looking around the house for the kids, the bottle is gone and the carpet is completely clean.
Continuity mistake: When the 2 characters are inside their house, there is a plate and mug on the table. Before the Reptar wagon is seen floating on the river, the mug and plate have disappeared.
Continuity mistake: When Chuckie breaks his glasses, they go from being broken to fixed between shots.
Continuity mistake: When Stu comes into the room with a crying baby Dill in his arms you can see that baby Dill wearing yellow pajamas. But in the next scene when they are singing the lullaby Dill is back in his purple pajamas.