This is based on opinion. Please don't list it on a work's trope example list.
Tear Jerker / Mary Poppins
The twins forgetting how to talk to animals when they both turn one year old.
Every time Mary Poppins leaves the Banks family, especially when she leaves the children mementos and reminds them that nothing lasts forever. When Jane and Michael ask Mary Poppins in the second and third books how long she will stay, she gives rather vague answers, making her departures unpleasant surprises for the Banks family. P.L. Travers claimed that even she cried when Mary Poppins left the Banks children for good in Mary Poppins Opens the Door.
Doubly so when you learn that "Feed The Birds" was Walt Disney's favorite song. He would frequently ask the Sherman Brothers to play it for him after their Friday afternoon strategy sessions. And then? They played it at his funeral. Y'all can go cry now.
And triply so when you learn, years later, that the bird lady was played by Jane Darwell, already no spring chicken when she won the Best Supporting Actress Oscar for playing Ma Joad in The Grapes of Wrath a quarter of a century earlier. It was her last film role.
Quadruply so when you learn that Darwell was one of Disney's favorite actresses, and he personally traveled to her retirement home to request that she be in the movie. That's saying something.
What makes it worse is when Mr. Banks goes past the cathedral as he makes his way to getting fired; a Dark Reprise (or perhaps regular reprise, since it sounded dark anyway) swells as he looks at the utterly empty steps of cathedral, then up into the air.
In fact, that cathedral scene is easily the biggest tearjerker in Disney history.
There is a not-small implication by the absence of the bird lady is that she passed away and that by denying his children to give their money to her and telling them to ignore her, they'll never be able to show the woman kindness ever again. That not only did Mr. Banks take his children for granted, but life itself.
Ultimately, the story of Mr Banks. He's a cold and selfish misogynist looking to be remembered in the world of banking. His life is turned upside down by the introduction of Mary Poppins, who brings fun to his family until he realizes what a failure in life he's been. He is ridiculed before his peers, sacked from his job, and then reconciles with his family, intending to spend more time with his children. And he recovers his job at the end!
Near the end, when Bert is describing George Banks's attitude towards his work and family (for emphasis, to a slow melancholy version of "The Life I Lead", where Mr. Banks had described much the same thing near the start of the film):
You're a man of 'igh position, esteemed by your peers And when your little tykes are cryin', you 'aven't time to dry their tears And see them grateful little faces smilin' up at you Because their dad, 'e always knows just what to do. You've got to grind, grind, grind at that grindstone Though childhood slips like sand through a sieve And all too soon they're up and grown And then they've flown And it's too late for you to give.
Mr. Banks opens the song with an equally sad statement to the position he's found himself in. The whole song, A Man Has Dreams, is pretty depressing.
A man has dreams of walking with giants. To carve his niche in the edifice of time. Before the mortar of his zeal has a chance to congeal The cup is snatched from his lips. His flame is snuff ab'rning. He's brought to rag and ruin in his prime.
When Mary Poppins finishes packing for her departure, then watches Jane and Michael go off with their parents without a backwards glance. Just because something is right and correct doesn't automatically make it less sad.
However, in Mary Poppins' view: "Practically perfect people never permit sentiment to muddle their thinking."
Oh, balderdash. Her umbrella didn't buy that line, and neither should anyone else.
When Michael and Jane run away from the bank and into Bert, who comforts them and he tells them their father loves them, and they say that he doesn't love them at all. Bert explains their father to them, and how no one is there for him, at the end of the day, and how Bert feels sorry for Mr Banks having a dead end job.
Michael: Father? in a cage? Bert: They makes cages in all sizes and shapes, you know. Bank-shaped, some of 'em, carpets and all.
When Michael apologizes for inadvertently causing the bank riot, and gives his father the tuppence, hoping it'll make everything better. Awwwwww.
Most of the above moments, but especially Mr. Banks' walk of shame to the bank, the empty cathedral steps, Bert's sad reprise of "The Life I Lead", and the kids being upset over Mr. Banks being "in a cage", all become even more of a Tear Jerkerafter viewingSaving Mr. Banks and understanding their significance and meaning to P.L. Travers.
The end of the Laughing Gas/Visit with Uncle Albert scene when Mary told the kids it's time to go. Which made poor Uncle Albert and Bert very sad.
Mary's departure and the moment when she says goodbye to Bert and kisses him on the cheek.
The reprise of "Being Mrs. Banks," where Mrs. Banks, after being cowed and uncertain for all of the play, reaches out to her husband with courage and love.
George, dear, I know it hurts your pride, dear, But you can't just run and hide, dear, for can't you see that I'm here, And I am on your side!
George's lament that precedes this, a Dark Reprise of "Cherry Tree Lane," is also a tear jerker
Illusions may shatter, but memories stay The things that really matter, I lost on the way. The sovereign, the master, and long may he reign The famous "good for nothing" of Cherry Tree Lane.