"I see now that the circumstances of one's birth are irrelevant. It is what you do with the gift of life that determines who you are." - Mewtwo

“Animals don't behave like men,' he said. 'If they have to fight, they fight; and if they have to kill they kill. But they don't sit down and set their wits to work to devise ways of spoiling other creatures' lives and hurting them. They have dignity and animality.” ― Richard Adams, Watership Down

That book does a really good job of presenting just how shitty humans are pretty much throughout, without coming across as being preachy or sanctimonious, and I like that.

Charlie and the Chocolate Factory, chapter 10 is pretty rough, particularly this stark line:

"Slowly but surely, everybody in the house began to starve."

I read the book to my daughter a few years back and I'd forgotten quite how bleak things are before all the fun stuff that people remember.

"Do you think God stays in heaven because he too fears what he has created?"

"I like you as you are Exactly and precisely I think you turned out nicely And I like you as you are

I like you as you are Without a doubt or question Or even a suggestion Cause I like you as you are

I like your disposition Your facial composition And with your kind permission I’ll shout it to a star

I like you as you are I wouldn’t want to change you Or even rearrange you Not by far

I like you I-L-I-K-E-Y-O-U I like you, yes I do I like you, Y-O-U I like you, like you as you are"

• Mr. Rogers

"If the world chooses to become my enemy... Then I will fight. Like I always have.",

Shadow, Sonic 06

Ozai: (bitterly) It was to teach you respect.

Zuko: It was cruel! And it was wrong.

Ozai: Then you have learned nothing.

Zuko: No, I've learned everything! And I had to learn it on my own.

Avatar: the Last Airbender

"They say suffering brings wisdom. If that is the case, then I intend to make you very wise."

Optimus Prime, Transformers Comics

"Man, don't you know? The law ain't made to help earthy cats like us. Here on our planet, back in the old days - back in the real old days - it was just every man for himself, scrooblin' and scrat-scroblin' for the good stuff, the greenest valleys. And the strongest, meanest men got the best stuff. They got the green valleys and were like 'The rest of you, y'all scrats get sand.' And that's when they made the laws, you see? Once the strong guys got it how they liked it, they said 'This is fair now, this is the law.' Once they were winning, they changed the rules up." —Jake the Dog, Adventure Time, "Ocarina"

Winnie the Pooh

"Sometimes the smallest things take up the most room in your heart."

Lots of good answers for ATLA, but I'm partial to the "Do the tides command this ship?" scene.

Maybe the best introductory scene for a villain that I've ever seen.

Avatar Legend of Kora, Varick says:

'If you can't make money during a war, you just flat-out cannot make money.'

Pretty much the entirety of the Animorphs book series, but I guess there was a reason for it. But for some kids books, holy hell.

"See, win or lose, right or wrong, the memory of violence sits inside your head. It sits there, like some lump you can't quite swallow. It sits there, a black hole that darkens hope, and eats away at everyday happiness like a cancer. It's the shadow you take into your own heart and try to live with."

The land before time. Littlefoot sees his shadow and thinks its his mother, realizes its not and that hes very very alone.

There's an argument to be made that Rocko's Modern Life was not for children, but it aired on Nickelodeon in the afternoon, so we watched it. And this is poignant as hell-

R-E-C-Y-C-L-E Recycle!
C-O-N-S-E-R-V-E Conserve!
Don't you P-O-L-L-U-T-E. Pollute the rivers, sky, or sea. Or else you're gonna get what you deserve

...I still sing it to myself sadly when I read the news sometimes.

"Fraggles don't have any bosses [...] We each lead ourselves and we all lead each other." - Wembley Fraggle, Fraggle Rock

"There is a difference between you and me. We both looked into the abyss. But when it looked back at us... you blinked."

--Batman, Justice League: Crisis on Two Earths (2010)

"Life is pain, Princess."

"Pay a man enough and he'll walk barefoot into Hell."

• David Xanatos, Gargoyles

"If you'll excuse me, I have some children to turn into corpses!" -Bill Cypher, Gravity Falls

"I demand a favor"

"I grant but one boon, mortal. And it will be given to you as it is given to everyone - when your time has come."

Gargoyles, Guy summons Anubis to bring back his son. YT Link for the amazing delivery.

"Death is always pointless - that is the point"

‘Everyone dies, some now some later’ from Princess Mononoke