Continuity mistake: In the episode "Petarded", when Peter is in court, when he says he is going to call "the ghost that never lies" to the stand, only Stewie is visible over Peter's shoulder. But when Peter says "But only I can see him", Meg is also visible over his shoulder.
Continuity mistake: In the episode when Peter finds out that he is retarded, in the scene where they are about to start shooting at each other, when Peter says, "Nobody fire at Lois. She's scared.", look over his shoulder. In the picture, Stewie is facing left. Later, when they're shooting at each other, Stewie is facing right.