Continuity mistake: When the bank executives are basically harassing Michael to give them his money, there is a shot where they are singing and marching forward and force the children to back into the wall. There is a pattern of large squares on the floor, and the men in the back are on the inside edge of the square. Then the camera goes out for a long shot so Mr. Dawes can talk about the banks of England. Now he is standing on the edge of the square. When he finishes his little speech, in the next shot they are standing back in the original position.
Continuity mistake: When Mary Poppins starts to read the "qualifications", the paper she reads from is whole, with no kind of indication that it had ever been torn. After a quick cut to George and back to the paper, the closeup of the paper reveals the lines where it was torn. Also in this scene, when she comes in, she has white gloves on. In the closeup on the paper, the gloves are gray, and a few shots later, they're white again.
Continuity mistake: When Admiral Boom makes his appearance, and asks about the time gun, he states "Three minutes and Six seconds" until the hour. However, the argument between Katie Nanna, the maid and cook, and Mrs. Banks' "Sister Suffragette" number, and Nanna's announcement of departure take a total of five minutes and ten seconds until the gun is fired.
Continuity mistake: When Mary Poppins is reading the childrens' torn-up note to Mr. Banks, she is wearing a pair of white gloves. The next shot is a close-up and she is wearing black gloves. And then finally a room shot, where she's wearing white gloves again.
Continuity mistake: When Bert is showing Jane and Michael his chalk sketches and doing his tightrope demonstration, you can see the pigeons in the corner on the far side of the bench. In the next shot when Jane points out the English countryside, the pigeons are right behind Bert again and walking away.
Continuity mistake: When Mary, Bert, and the children enter the tea parlor and see Uncle Albert floating by the ceiling, the camera cuts to Bert behind Mary, then Bert in front of Mary (Bert preparing to laugh and levitate), then a shot of the children shows Bert behind Mary again. Bert cannot move this fast in a split second.