Continuity mistake: As Max is carrying a birthday cake out of the kitchen, the candle blows out as he walks. But the candle is suddenly lit again when the camera angle changes, as he walks into the living room.
Continuity mistake: The rabbits have a close encounter with some rats in a shed on the cemetery. A spade falls over. In the next shot the spade lays in a wheelbarrow.
Factual error: In the 1953 sequence when the headmaster is driving Fiona and Paul home, the yellow car parked in the road is a Vauxhall Viva HC, which didn't start production until 1970.