Factual error: Mr. Dawes Jr. states that the tuppence (two pence) invested by Michael grew into enough to pay off the mortgage on the house. Interest rates over that 20 year time period were about 4%, which would have made that 2p grow to all of 4p. Go nuts and assume an impossibly high return of 15% per annum, compound, consistent over the twenty years. Despite the fact that not even Bernie Madoff offered ridiculously high returns like that, after twenty years the original two pence investment would be worth 39p. As an aside, houses of the time cost about £750, far below current London prices, but still considerably more than 39p.wizard_of_gore
Other mistake: As established in the original and this film, when the Admiral fires his cannon, everything in the house falls off walls and mantles, and everything needs to be caught to prevent them from being damaged. However, when he fires his cannon as Mary Poppins and the children are going out to have the bowl repaired, Michael has already left for work, Jane and Ellen are standing outside, and Mary, the children, are getting onto Jack's bike - leaving no-one in the house to catch the falling objects which would therefore all be smashed or damaged.
Other mistake: The snow globe from the original is in the loft in the new film, but in the original film, as Mary was leaving the Banks house while they flew a kite, she packed it in to her carpet bag.
Factual error: When Mary and the children go to the bank the long shot of the bank shows a statue that was not erected until 1994.