Most of the Warhammer 40,000 novels focusing on the Imperial Guard portrays them as actual humans rather than statistics to Zerg Rush with. Perhaps taken to extreme with the Ciaphas Cain novels, which are distinctly comedic against the ridiculously GRIMDARK setting.
Likewise, the Gaunt's Ghosts novels, while still fairly dark, portrays the Imperium in general working order with a healthy dose of optimism (a concept often completely unheard of in the 40K universe).
The Earlier versions of codex was essentially one huge Satire, and then the American teenagers bought it into the GRIMDARK and well...it got darker.
And now in 2018, there's going to be Warhammer Adventures which aims to introduce 8-12 year olds into the Warhammer 40K and Age of Sigmar backgrounds. The emphasis will be on adventure and lessons in courage, friendship and diversity (um..what world is this again?).
The spinoff trilogy of the Petaybee books, featuring Action Girl Yanaba Maddock's children, are far less dark than the originals.
The original fairy tales of The Brothers Grimm were quite grim indeed. The versions published and told to children today are much lighter and less gory than the originals. This trope was played with, as the Grimm Brothers simply collected tales already in existence. Some were lightened (Little Red Riding Hood), some were darkened (Cinderella). The Charles Perrault version of Cinderella, which preceded the Grimm version by nearly 100 years, was adapted by Disney.
Charles Perrault's Sleeping Beauty (properly titled "The Sleeping Beauty in the Wood") was based on the earlier tale Sun, Moon, and Talia. Sun, Moon, and Talia is a dark story infamous for the princess being raped by a king who is cheating on his wife, who tries to eat the resulting children. Perrault's Sleeping Beauty is much cleaner, with the princess getting a proper Prince Charming to rescue her from her enchanted slumber, the couple's children being born after they get married, and the evil wife is replaced by an ogre mother-in-law. It's still darker than most modern versions, though.
Pish, Posh, Said Hieronymus Bosch is a 1991 children's book which depicts the medieval artist Hieronymus Bosch as a Cloud Cuckoolander who has an array of surreal creatures as his companions, and not as a person who painted singularly bleak and moralistic visions of Hell.
Fate of the Jedi fits this trope. Yes, there's Force psychosis, an Eldritch Abomination, and attempts on the Solo family's lives in order to discredit not one but two heads of state, but when you consider Legacy of the Force had a teenage boy join the GFFA equivalent of the Hitler Youth, consider cannibalism, almost fall to The Dark Side, lose his mother (which drives his father into a deep depression, contemplating suicide), and be tortured, molested, and forced to watch his mentor figure die, yeah.
The Deptford Mouselets series contains considerably less violence than the books in Robin Jarvis's Deptford Mice trilogy from which they spun off. There are still some frightening moments, but little to no gore, and their tone is more lighthearted.
The Last Dragon Chronicles spin-off series The Dragons of Wayward Crescent, focusing on the dragons themselves, is written for very young readers.
Chronicles is a rehashing of Books of Kings to highlight Israel's achievements and give hope to the Jewish exiles in Babylon.
Oceanology [Part of the "Oology" series that began with Dragonology] is this to 20,000 Leagues Under the Sea— Land and Aronnax board the Nautilus willingly as part of an organized and publicly-advertised scientific expedition, Nemo doesn't sink any ships or kill sperm whales, and there's no mention of his family being dead. (Nemo still does turn out to be crazy and does try to stop them from leaving, though.)
Fear Street is a series of horror books intended for teenagers, and often contained violence and death. However, its author became more famous for his kid-friendly Goosebumps books, so a Spin-Off called Ghosts of Fear Street was created. It was also set in the town of Shadyside and centered around the titular Fear Street, but the protagonists were all pre-teens and their circumstances were generally much tamer than anything that happened in the main series.
The Rainbow Magic First Reader books are slice of life tales that don't include villains.
Henrik Drescher's children's book Love the Beastie is much lighter and softer in tone than its predecessor Patthe Beastie due to Paul and Judy treating their pet Beastie in a more friendly manner rather than torturing the Beastie like they did in the first book.
The Hunger Games: The arena for the 50th Hunger Games (the Second Quarter Quell): The Cornucipia sitting in the midst of a sweet-smelling green meadow, and the sky was azure blue, with fluffy, billowing white clouds. There was a snowy mountain and a forest, squirrels and butterflies and flowers and pinky birds. And even food growing. However, it was actually a Death World: carnivorous squirrels, butterflies with stings, killer birds, poisonous flowers, the mountain was a volcano.
Darkest Powers is the young adult spinoff to The Otherworld series and shares its universe. It is slightly toned down for a teenage audience. The sexual elements have been removed, as have profanity, but it's still rather violent.
The Doctor Who Novelisations by Terrance Dicks often softened more mean-spirited elements of the plots to fit what Dicks considered to be the show's moral code. An obvious example is in his version of "The Sunmakers", where, after murdering the oppressive government official who is driving them to suicide, the rebels feel like they have done something awful and express shame that it was necessary. In the original story, after they kill him, a huge cheer goes up and the people immediately start partying.
Seeker Bears is pretty tame by Erin Hunter standards. Sure, characters have Family Unfriendly Deaths, however they're few and far between. This is in strong contrast to Warrior Cats, which features at least three major deaths per book (and often in graphic detail). The violence is also toned down compared to its sister-series'. Characters don't bleed that much despite all their clawing and biting.
In the Black Jewels series, the two "Cassidy books" (The Shadow Queen and Shalador's Lady) are like this compared to the original trilogy. The world has already been saved, so there's more narrative focus on healing, rebuilding, and dealing with smaller problems. There is much less on-screen violence and abuse, and main characters' traumatic backstories are less overwhelming than those of the original protagonists: Gray in the Cassidy books was held prisoner and tortured by an evil Queen for a few years as a teenager, whereas Daemon in the original trilogy had been a Sex Slave for centuries. And the cute little talking Shelties get more page time.