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.
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. Partially subverted, 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-type, 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.
Oceanology [Part of the "Oology" series that began with Dragonology] is this to Twenty Thousand 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 Lovethe 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.