WARNING: The following is a crackpot media theory not meant to be taken seriously. Side-effects can include paranoia (especially regarding British accents and nannies) and destruction of personal childhood. Reader discretion is advised.

Mary Poppins.

Rosy-cheeked nanny, or cunning fey terrorist?

We are meant to see the film as a fantastic but touching tale of a father discovering the importance of actually raising his children and not treating the world with the same rigidness of his career, but is there more to this story than meets the eye?

Whatever Mary Poppins is, she's clearly not human. We're introduced to her sitting on a cloud calmly doing her makeup with her bag and umbrella situated next to her. She manages to magically (telekinetically?) retrieve a ripped-up letter from Mr. Banks' fireplace, and arrive by magical umbrella while blowing away nearly a dozen old ladies (aspiring to be Mr. Banks' nanny as well). The other potential nannies are likely injured if not outright killed by this feat, or, since we never hear from them again, it's possible they were wisked away on the wind off the face of the earth.

For simplicity's sake, I will try to use terms from White Wolf's Changeling, although there might be a few discrepencies.

Mary Poppins is likely a Sidhe, an elegant noble fey spirit known for their beauty as well as their arrogance. She even refers to herself as "Practically Perfect in Every Way" and says it as if it's an indisputable fact. She has a wide variety of magical charms and treasures at her disposal, including a talking umbrella, a handbag which either is bigger on the inside than on the outside or can actually produce desired items for Ms. Poppins, a tape measure that seems to give almost sarcastic "measurements" regarding a person's personality and disposition, and a mirror which contains a reflection that acts independently of her. (Ms. Poppins refers to the mirror as "cheeky.") It's entirely possible that the mirror is the root of some sort of undisclosed weakness of Ms. Poppins. She also displays numerous charms, including gravity-defying stunts like sliding up, down, and across the banister, minor legerdemain tricks with a snap of her fingers to tidy things up (a trick she somehow manages to pass on to the two children as well), and a silver tongue used to befuddle Mr. Banks and the children on numerous occasion, even hypnotizing the children to go to sleep when they otherwise refuse.

Mary Poppins has numerous contacts who also display supernatural characteristics, likely fey creatures themselves.

The most prominent of which is Bert, a vagabond with various oddjobs including a one-man band street performer, a sidewalk artist, and a chimney sweep. Whether he handles all these jobs at once, gets routinely fired or quits from his current job, or simply does all of these for fun is unknown. Bert is likely a Pooka, though a benevolent one by appearance. His words are usually colorful and exaggerating, often to entice the children (and therefore Mary Poppins) on a fantastic adventure. Either he is using his silver tongue to convince the children to come with him (Mary Poppins usually seems reluctant), or these adventures are machinations by Poppins' herself, which makes Bert just as deceitful about his intentions if not moreso. It's even implied by the song "Jolly Holiday" that Poppins and Bert might share, have shared, or will share at one point a romantic relationship.

Other such spirits include Uncle Albert, whose hospitable nature might make him out to be a Boggan, though a peculiar one at that. There's also the bird woman who fits the role of a Sluagh, a keeper of secrets who clings to the shadows. The Chimney Sweeps could be Pooka like Bert, but they could also be Eshu, wandering storyteller vagabonds, or perhaps a more likely suspect , the revelling Satyrs.

Less likely to be one of Mary Poppins' cohorts but still a likely fey is Admiral Boom, who along with his assistant Mr. Binnacle live on a ship affixed to the top of a house (which no one seems to find odd) and blast a cannon at certain times (which even more strangely no one seems to odd). Admiral Boom and his assistant could be Nockers, known for their affinity with gadgets and explosions, but the lack of swearing could suggest that one or both could also be Trolls, militaristic guardian knight-like fey, perhaps in charge of defending Cherry Tree Lane from unwanted Unseelie Fey like the chimney sweeps.

Now back to the actual plot. Mary Poppins shows up at Mr. Banks' house after "dispatching" a long line of prospective nannies, and practically forces herself into the position with her silver tongue and confounding Mr. Banks with the letter he'd torn up previously. Mr. Banks reluctantly accepts thinking it was his idea all along.

After winning over the children with her parlor tricks, Mary Poppins proceeds to take the children on a series of outings, each time detouring from their original destination to some fantastic scenario. First, they enter a sidewalk drawing by Bert into an animated realm (likely part of the Dreaming) where they ride carousel horses off the carousel and, most importantly, Mary Poppins introduces the children to a certain word (not posted here for safety concerns). Their second outing ends up detouring to the residence of Uncle Albert who has apparently come down with a serious case of laughter, or rather come up since he's floating near the ceiling. The laughter infects Bert and the children who also float up. Mary Poppins remains unaffected by the laughter but floats up anyway along with a table and tea set so they can have a tea party near the ceiling. The children are introduced to several jokes which cause massive fits of hysteria disproportionate to the actual comedic value of the joke. The word and the joke will both come into play later.

Mr. Banks is displeased at the fantastic tales of his children and "the word" is being sung throughout the house making everyone more cheerful. Even the maid and the cook who famously bickered are cheerful towards one another. Mr. Banks aims to fire Mary Poppins, but Poppins twists the conversation around so that instead of getting fired, Mr. Banks promises to take the children to the bank the next day. That night, Mary Poppins sings a lullaby about the Bird Woman who sits on the steps of the cathedral Mr. Banks walks by each day. It is likely that this lullaby like her previous one is subliminally influencing the children, as is shown next day when the boy, Michael, is obsessed with "feeding the birds" for "toppins a bag," but Mr. Banks refuses to let his son spend his money on such frivolities. Instead he, along with the senior bank staff, attempts unsuccessfully to teach the children the value of the banking system and the British economy. When the bank manager, Mr. Dawes Sr., takes the toppins from the boy's hand prematurely, the boy throws a loud fit that sends all the other bankers into hysteric fits thinking the bank has no more money and inducing a panic similar to the stock market crash.

The children run off to be found by Bert, likely waiting for them. Bert brings them home and is "invited" by Mrs. Banks to watch the children as she has a political engagement to be at. Bert seemingly reluctantly enters, but then proceeds to open a portal and "accidentally" transport the children to another fantastic world. While we and the children are told they are merely on the rooftops of London, the surroundings and sky do not match what we see outside the Banks' residence, so this "realm of chimneys and soot" is likely another area of the Dreaming. They explore the area a bit and eventually run into a band of chimney sweeps, or rather, Bert summons them. These chimney sweeps could be Pooka, Eshu, or Satyrs as previously mentioned, or they could be a separate brand of spirit altogether native to this realm.

Admiral Boom sees the revelers from his ship and fires a volley of fireworks at them, forcing them back down the portal into the Banks' residence. This is likely a cunning plot by Poppins and Bert to a) establish an easy fey entrance into the Banks' residence for future use, and b) release the revelling Chimney Sweeps all over the streets of London. They do so manipulating the revelling nature of the Chimney Sweeps and the protective nature of Admiral Boom. Mr. Banks, emotionally drained already by the day's events, is called back into the bank to what likely will be the termination of his employment.

Finally, after Mr. Dawes Jr. ceremoniously rips up the flower in his suit, inverts his umbrella, and destroys his hat, Mr. Banks breaks and starts recanting his children's various exploits, saying "the word" over and over again as well as telling "the joke" before leaving the bank singing madly.

The movie ends with the father seemingly having mellowed out and goes to fly a kite with his children, where he meets the other bank staff members who give Mr. Banks a promotion and mention that Mr. Dawes Sr. died laughing after eventually getting "the joke." Mary Poppins then takes her leave as "the wind changes."

"The word" is likely magical in nature, perhaps a charm spell or makes the user (or the recipient) more susceptible to fey magic, getting even the rigid banking staff most likely teeming with banality, to fall for the charms. "The joke" although amusing isn't so funny as to kill a man, so probably the way its told is another such charm that can induce hysteric fits of laughter that can cause a person to levitate, and in the case of Mr. Dawes Sr.'s frail constitution, kill a man.

So to recap, Mary Poppins' short-lived stay accompished the following:
  • [1] Assassinated an important figure in the British economy.
    [2] Installed Mr. Banks as a prominent member in the bank and therefore the British economy, and did so in a way that makes Mr. Banks susceptible to Mary Poppins' suggestions.
    [3] Caused an economic crisis as people lose faith in the bank (apparently it was so bad the last time the bank took a hit this hard was when a shipment of tea they financed was throwin into the Boston harbor).
    [4] Released a pack of revelling vagabond Chimney Sweeps onto the streets of London.

One or more of these could have been her ultimate goal (or part of a larger one), to break down and/or eventually control vital parts of the British economy. We already know from her list of contacts that she has an interest in the poor members of society, and likely a massive economic shift could benefit them. There's also the possibility this was all a massive plot to assassinate Mr. Dawes Sr., likely unreachable in his bank due to all the banality in its walls. We're likely only seeing part of a much larger plot that may make more or less sense when viewed as a whole, but either way I must caution you to be wary of rosy-cheeked British nannies who describe themselves as "practically perfect in every way."