Billy's coming out to his parents, even if it was a Funny Moment. It could easily have been played for drama and follow the traditional coming out tropes, but instead Heinberg opted to have Mr. and Mrs. Kaplan happily support Billy and warmly welcome Teddy to the family!
In Children's Crusade, the Scarlet Witch regaining her memories & being informed that Wiccan & Speed are her long thought lost children and the reaction of the pulled through time Scott Lang to his daughter Cassie following in his footsteps.
In Children's Crusade 9, after Billy sits around moping for months, over the events of the Children's Crusade arc, Teddy proposes to Billy, and the two kiss on-panel for the first time.
And then Ms. Marvel interrupts them & tells them that Captain America wants them at Avengers Mansion in costume, where he tells the remaining members of the team that even if they no longer operate as Young Avengers, they are going to be considered full Avengers from this point on.
The alone-time moments between Billy and Teddy in the 2013 volume are very heartwarming on both sides.
A small moment, but in the 2013 volume, when the group is attacked by the alien parasite Billy accidentally summoned Billy immediately puts himself between their attacker and Loki and protects him with his magic. Considering up to this point the team has no real reason to trust or defend Loki, it was really touching. Loki's shocked expression really seals it. In spite of all his manipulations, the God of Mischief really can't understand why Billy's protecting him!
Volume 2, issue 13 is chock full of heartwarming moments.
Prodigy talks some sense into Teddy about his relationship with Billy.
David: Listen. Yes, he could have accidentally wished you into existence. Existential nonsense. Who cares? It doesn't matter. You're you. He's him. Your love is as real as anything I've ever seen.
David: Teddy, listen. A magical power someone else has over you for no reason you can really justify but cascades through you until every cell cries out for his touch? What do you think loveis?
Teddy and Billy make up, Billy in turn destroys Mother and fixes the multiverse.
America is seen with tears streaking down her face and opens the portals that allow Billy to fix his error.
Billy introduces the gang to his parents.
When Billy goes full Demiurge, one panel shows America with tears running down her face making star sign with her hands. Her people worship the Demiurge as their god... after months of seeing Billy as just another angsty teen, she's literally watching the birth of her god and doing the equivalent of crossing herself.
America's tendency to call Kate "Princess" is Heartwarming in Hindsight because America herself is a Princess and she was trying to be friends with Kate.
A Meaningful Background Event in the last issue, Billy gratefully hugging Tommy after the party and Tommy just looking completely confused.
Noh-Varr's face when he chooses not to play "Be My Baby" at the party, and puts on "Get Lucky" instead, mainly because he's finally processing his feelings about Kate and realizing it's not all about him.
The ending frame of Volume 2 is Loki liking a photo on Instagram the group took of themselves. Doubles as a Tear Jerker.
In the one-shot Winter Soldier: Winter Kills, Eli, Kate, and the Vision cross paths with Marvel's original kid superhero, Bucky Barnes. They get off to a rocky start, because Bucky treats them like kids and unintentionally uses a homophobic insult towards a bad guy, which offends them on Wiccan and Hulkling's behalf. Once Nick Fury vouches for everyone, though, they team up and Vision suddenly realizes who Bucky is, once he compares his facial scan with the historical record. They track Bucky down again, and, to his surprise, salute him.
"It's been an honor, Bucky. For all of us."
Later in a follow-up during Young Avengers Presents, Bucky, the new Captain America, comes to pay his respects to Isaiah Bradley. Eli immediately guesses it's him, as the existence of the black Captain America is really only talked about in the black community— Captain America's sidekick is the only living white guy who would really know he existed. Eli tracks him down as he's having an existential crisis (due to the fact that, despite calling himself Patriot, he's not very proud of America's history and actually resents a lot about the country). Bucky welcomes the kid in, and gives him some advise on how Steve, too, often wasn't very proud of America's history, but being a patriot isn't about My Country, Right or Wrong, its about striving to make the country as good as it could be. It certainly leads to a neat Odd Friendship.
A small one, but after Quicksilver "kidnaps" Billy, the way Billy smiles when Tommy catches up to them is really sweet.