Why does Mary Poppins only say "practically perfect in every way"? Because true perfection is impossible and Mary's being humble, acknowledging that everyone has room for improvement.
Why does Ellen have no free time to watch the children on Mary Poppins's day off? Because she's the one who has to mind them while they're between governesses, so she's likely behind on all her work and only just getting to catch up since Mary arrived.
Why did all the people and talking animals in the chalk-drawing world admire Mary Poppins so much? Because they were created by Bert, and therefore expressions of his own mind!
Maybe good luck did rub off when all those chimney sweeps shook hands with George Banks-It would help explain why the bank re-hired him so quickly near the end of the movie.
Mr. Banks has a whole song about how he loves everything being just so, arriving home at six, with his slippers, sherry, and pipe ready at six oh two, and such. Why isn't he concerned by the antics caused by Admiral Boom's cannon salutes? Because that is part of his routine as well. Admiral Boom is nothing if not famously punctual, after all. And the perspective is not at all unlike that held by people living in dangerous places, such as soldiers in a warzone who might treat enemy raids as just part of the nine to five, as it were. "Normal" is a matter of perspective.
The Admiral fires at 8 AM, but earlier than 6 PM.
Well, there's this, too: He's never home to deal with the falling objects, at least not in the evening. Notice how the song goes: "At 6:01, I march through my door!"
"Oh, father, every one of those sweeps shook your hand! You're going to be the luckiest person in the whole world!" Could be just an innocent childhood thing to say, with particularly bad timing to boot....but getting your perspective straightened out and your job back after being fired is pretty lucky.
All of Mr. Banks's songs have the same tune except Let's Go Fly a Kite. There might be a reason for this: he's not very interested in things which don't have some objective importance beyond simple entertainment up until he realizes the value of fun. So when he feels the need to sing, he just uses the same tune because he probably doesn't value creativity enough to make separate tunes. However, by the time he's singing Let's Go Fly a Kite, he knows the value of entertainment and thinks that some variety in his tunes would be more entertaining.
Is he? The movie is set in 1910, and conscription in Britain during WWI applied to men aged 18-41 and was in effect through 1918; If Michael Banks was eight (the age of the actor at the time of filming), he would have either been recruited at the very end of the war or narrowly missed it all together.
Boys under the conscription age frequently attempted to join the war. Many succeeded. Worse still, when generals started to realise the dire situation for Britain, they started illegally allowing it.
Even in real life the actor who played him died at 21 (of hepatitis).
Even had Michael not died in the war as a soldier, he, Jane, or any British child of that generation (as nonfictional children had) would have been affected by the war(s) to come one way or another. Particularly where the bombings of World War II were concerned.
Fortunately, Mary Poppins Returns shows that Jane and Michael lived past WWI, and started families of their own.
Bert is definitely old enough to have fought in WWI.
So is Mr Banks.
What happened to all those people and talking animals in the chalk-drawing world when the rain came?
Maybe the painting was just the gate to that world?
Or maybe it was a fucking chalk drawing. It's possible that the chalk world sequence was just a surreal metaphor for the experience of viewing art.
The presumption that it is otherwise suggests that 'Mary Poppins is God' and can create living worlds.
It was definitely something unpleasant for those not "native" to the drawing. When the rain began, Mary not only said "Stay close" to the children, she pulled them in as tightly against her as possible — implying they might have been washed away with the chalk (or trapped in a crumbling world like Vanellope in Wreck-It Ralph) if they weren't safely inside her magical aura.
The use of children for chimney sweeping was outlawed decades before 1910, in fact the equipment Bert is carrying when he meets the Banks kids after the bank run was created specifically to replace child labour.
A much more mild example - Just how many fragile things (including fish) were knocked to the floor before Ellen, cook, and Mrs. Banks figured out the "POSTS EVERYONE!" routine?
On that note, it's a good thing Mrs. Banks has not herself been arrested and thrown in jail for her suffragette activities - they'd be down one post full of valuables.
Watching the movie as an adult, it was shocking listening to Chim-Chim-Cheriee and realizing that it was a song glorifying pollution. No, seriously, listen to them sing about the glory of London covered in smoke "hardly no day and hardly no night". It ties back to Song of the South's Zippa-De-Doo-Da in finding the good in everything, but it's still shocking at the horrific pollution of the Disneyfied Edwardian London, orders of magnitude worse than anything found in Europe or America today.
I always assumed it was just about dusk/dawn, but I admit I hadn't seen the movie for years, only hearing the songs.
The "Let's Go Fly A Kite" song makes it even Harsher in Hindsight: up through the atmosphere / up where the air is clear along with the metaphorical desire to be lighter than air and flying around like the kite.
When the head maid stumbles in on the Chimney Sweeps barging into the Banks' house, she screams "They're at it again!" This isn't the first time that dirty, grimy chimney sweeps have jumped into the house and dirtied everything with their dance parties?!
Combine Michael's disgust at nannies who smell like "barley water" and George's reference to Katie Nanna having a "liver complaint" and you can see why she was so bad at keeping the children from running off: Jane and Michael were being taken care of by a drunk.