Prehistoric Planet / Heartwarming

Season One

Coasts

At the end of the episode, the reason for why the female Tuarangisaurus was swimming so sluggishly is revealed to be because she's pregnant with a baby. After a tense confrontation of her pod against the mosasaur Kaikaifilu, she finally gives birth without complications, with the baby taking its first breath and successfully joining the pod. Quite a sweet way to end the program considered how it started.
The portrayal of the Tyrannosaurus rex family is also pretty adorable in itself despite the initial tragedy, seeing the father peacefully scavenging a dead Archelon while the baby rexes playfully learn hunting skills at the beach under their father's watchful eye.
In the Tethydraco colony the ridiculously cute juveniles can be seen chirping at the adults.
The ammonite mating season is a marvel to behold, with them flashing waves of bioluminescence in sync as the pair up with their mates, showing an otherworldly beauty to a much-ignored species.

The Mononykus. Just the Mononykus. Easily the most adorable dinosaur to ever appear in a paleo-documentary, everything she does is bound to make you go "aww": from her shaking off termites while feeding from a log, to her scurrying around in the rain and finding shelter in a cave, to her utter bewilderment at the sudden influx of plants in the rainy season and her resulting scramble to catch bugs in the greenery.
The Tarbosaurus trio asleep in the sun after a meal are oddly endearing. And when they wake up and head to the oasis, they're seen peacefully having a drink and ignoring all the other dinosaurs at the watering hole: showing that they, too, are just ordinary creatures with mundane needs.
The courtship between the sneaky male Barbaridactylus and one of the females is rather endearing.
The Secernosaurus migration is a more nuanced portrayal of hadrosaurs often relegated as mere fodder for theropods in most documentaries. Here, they get more focus in their segment, and are even shown using the stars to navigate, portraying them as a smarter and more complex creature than what hadrosaurs are typically shown being.

At a riverbank, the old Tyrannosaurus is confronted by a female of his kind, but instead of fighting, he performs a courtship display and the two affectionately nuzzle, finding each other suitable mates. Quite a break from the Prehistoric Monster T. rex is usually depicted as.
The mother Quetzalcoatlus caring for her nest, with a timelapse of her effort over a span of days, and even fighting off a rival female who preys upon her eggs.

The baby hadrosaur that falls into the river makes it out alive and reunites with its family, being a rare instance in the series of a baby dinosaur not dying for once.
The dromaeosaurs are shown nuzzling each other when they reunite, and are later seen amicably sharing a hadrosaur carcass without any conflict.
While some Olorotitan babies die to the mosquitoes, one that falls behind finds the strength to keep going and happily reunites with its mother at the edge of the valley.
The Antarctopelta, after being evicted from the cave by his siblings, finding a safe and cozy home to stay in: a beautiful cave lit up by bioluminescent insects.
When the wounded Pachyrhinosaurus bull is cornered by the Nanuqsaurus, two other Pachys rush back to try to help. Sadly they fail and the old bull ends up being killed, but it still shows how bonded the Pachys are at defending their kin from danger.

The male Carnotaurus and his adorable mating displays, of special note as a very rare portrayal of the Carno in non-predatory behavior. In the end, he Did Not Get the Girl, but he tried his best.
The baby Triceratops, after getting lost in the dark cave and crying out for its family in a tense sequence, is eventually reunited with its family and safely makes it out alive.
The almost awestruck way the baby Therizinosaurus watch their adult counterpart effortlessly get honey from a bees’ nest. It's hard to say if any of them know that one day they too will be that large and powerful, but they seem to truly admire its strength nonetheless.
Despite the series taking place at the very end of the Cretaceous, the final episode doesn’t end in everyone dying in the K/Pg extinction event—instead we watch the Hatzegopteryx fly off triumphantly into the sunset.

Season Two

The Kuru hatchlings playfully investigating the Corythoraptor egg are positively squee-worthy, especially since they seem so adorably confused as to what their mother intends them to do with it until they accidentally break it by rolling it off the edge of a rock-shelf.
The squeaking sounds that the baby Isisaurus make are too adorable for words.