Continuity mistake: The father tears the children's advert for a nanny up into 8 pieces, but when it comes out of the chimney it's in far more bits.
Continuity mistake: At the beginning when Mrs. Bank is talking to Katie Nanna you can see the clock behind her and you can clearly see that the time is 6:30 when a little later it is at 6:00.
Revealing mistake: An early scene with the constable and the children, Jane silently mouths along with one of Michael's lines.
Continuity mistake: At the bank where the elder Mr. Dawes appears from the back room, he makes it as far as the edge of the step in that shot. In the next shot, he's back by the door walking again to the edge of the step.
Continuity mistake: When Uncle Albert, Bert, and the kids fall down from hovering on the ceiling, they're about to land on the chairs. But when the camera view changes, they land on the floor.
Other mistake: In the ceiling tea party, Mary Poppins offers Bert some sugar, and when he responds that he would not like any, his Cockney accent is gone.
Revealing mistake: When all four actors are up on the rooftops, look closely at them when they all step onto the smoke platform that brings them down. All four actors are doubles.
Revealing mistake: When Mary Poppins takes the children on an outing to the park, look at the front steps when the front door opens. They are not steps but flat ground painted to look like steps.
Revealing mistake: In the tea party on the ceiling sequence, 2 shots after Uncle Albert tells his long underwear joke, Jane does a backflip in the air. If you look closely you can see the imprints that wires that she was hanging from made on her dress.
Continuity mistake: At the end of the film, Mary Poppins flies away from the Banks's house (supposedly within a short distance of the City of London), however, she is then shown flying towards the City on a route that would take her over the Banks's house on the way, had she not already flown over it.
Revealing mistake: In the scene where Mary Poppins is removing the large plant from her carpet bag, Michael inspects the underside of the table, where the table leg casts a shadow across his face. When Mary crosses in front of him (still under the table) she does NOT cast a shadow, although she should.
Continuity mistake: When the kids meet Bert as a pavement artist, he draws a road with a single-arched bridge on his drawing. When they jump into the drawing, the bridge is double arched.
Revealing mistake: At the very beginning of the movie, when Mary Poppins is sitting on the cloud, you can see the string attached to her bag just as it almost falls through the cloud.
Continuity mistake: When Mr. Banks begins singing "Let's Go Fly A Kite," Ellen the maid puts her left hand up to her cheek in surprise. In the very next shot, her hands are clasped in front of her.
Factual error: The local police constable wears the divisional letter 'H'. H Division of the Metropolitan Police covered Whitechapel. While it is never specified where the upper middle-class Cherry Tree Lane is, it's certainly not in Whitechapel, which was a solidly working-class district in the heart of the East End. He also wears his letter and number on his helmet plate, a 19th century practice that had been abolished by 1910.