All the dinosaurs who managed to make it to the nesting grounds. When Aladar smiles at everyone and says "Welcome home", that hammers the heartwarming part home.
Neera managing to stop Kron from killing Aladar and goes with him to the right path to the nesting grounds. The herd sees them and follows their new leader, leaving Kron behind.
The courtship scene, before everything goes to hell. The music, the palpable happiness, the rush from the swinging lemurs while the adults not courting watch from below...
Aladar's methods for dealing with Kron's tyranny are, up until the last desperate moment, nonviolent ones. When he hears the older dinosaurs are being driven too hard, he asks in a kind, friendly manner for the pace to be slowed. And when Kron intends to leave his friends to be killed to slow the carnotaurs down, the audience expects Aladar to charge him. Instead, he races up to Kron and... turns to face the herd itself. Until he has no other choice he tries to appeal to people's better nature. Plio raised him right.
Aladar: HOLD IT! That could be you back there!
Even when he does finally confront Kron directly, Aladar still tries to do it without a fight. He only fights when Kron attacks him for usurping his authority.
Aladar really isn't the stereotypical couraeous young fantasy-adventure hero. Right from the very beginning, hi courage is... quieter. Aladar is a protector, a comforter, a peacemaker, and a nurturer. He sums it up himself.
Aladar: Look, Neera. We look out for each other, we all stand a chance of making it to your Nesting Grounds.
Neera: *mirthless laugh* You sound so sure.
Aladar: I'm not! ...But it's all I know.
Any time Plio is being maternal—quietly telling Bruton that he can survive if he doesn't give up, adopting Aladar and raising him to be the man—well, iguanodon—he becomes, and of course her relationship with her daughter Suri.
Suri: ...They're all... gone.
Plio: Gentle now... Shh. I'm here.
Yar, at the very beginning, couldn't kill a helpless infant even though his mind told him he had to. Points go to Plio, as well, for having complete faith in her father's good heart. She's not concerned for a moment that he might really do it.
Suri and her 'little Aladars', making sure the frightened babies got water.
Everything about Aladar finding water, but perhaps especially the way he planted himself beside Eema—temporarily too weak to stand—to protect her from being trampled. And on that note, the fact that he saved the entire herd simply because he took the time to stop and try to care for a fallen older dinosaur, and that let him realize that the water table was just a foot or so below the dry lakebed; and his first act after figuring it out is to immediately share the knowledge with the others. Neera's slow, thoughtful pan between Aladar and her brother (who's violently driving any and all comers away from the single water hole Aladar had time to dig, until he's had his fill) says everything.
"That's right, keep pushing and shoving! That's very helpful!"
It's subtle and likely unintentional, but when the straggler group sleeps, Aladar and Bayleen on the outsides form the shape of a rough heart.
Bayleen revealing how much Aladar's respect for the stragglers meant to her when he finally loses hope after struggling and struggling to reach a dead end.
"And the worst of it is... you allowed an old fool like me to believe I was needed. That I still had a purpose. And do you know what? You were right. And I'm going to go on believing it! I, for one, am not willing to die here."
Neera slowly learning how to hope again. After watching her nursery of orphans die off over the course of the movie—from a huge crowd in the beginning to just a single pair of brothers by the end—she goes back and helps to save the very last ones. You can hear in her voice that she's finally realizing maybe things don't have to be as brutal and heartless as Kron has always preached. Maybe showing mercy and caring for the weak really is worth it.
"Don't worry, little ones. You're going to make it."
The fact that the first 'little Aladar' was willing to be left behind by the herd rather than leave his weaker brother to die. He was desperately trying to push the fallen baby back onto his feet even as everyone around him ignored his cries for help. And then Neera came back.