Note also the spell which caused this also prevented aging, and took effect on everyone in Oz at the same time; this means that any babies in Oz are eternally babies, and that anyone who was at the moment of death is permanently caught there, and so on...
If I'm not mistaken; I believe it was said that everyone has an age that is "right for them". They age normally until they reach that point and stop.
Oz suffers from a ghastly Continuity Snarl, so it is possible that was said, somewhere. But there were definitely books in which it was stated that babies would be babies forever.
Many of Hans Christian Andersen's tales are less than child-friendly, as most of them feature heartbreaking things happening to likeable/tragic/etc. characters (or objects, as the case may be). "The Little Match Girl", anyone? Or the original "Little Mermaid"? And then there's "The Steadfast Tin Soldier". The story "The Fir Tree", while marketed as a children's story in modern times, has one heck of a Family-Unfriendly Aesop. A fir tree is disgruntled with its happy life in the woods, is jealous of the trees that get cut down as Christmas trees, until it eventually is cut down and decorated for a rich family. After the holidays the tree is promptly thrown into the attic to turn brown and die, is dragged out of the house and stripped of the ornaments, and is then chopped up and fed to the fire (complete with sound effects of the tree being chopped and burning up in a 1950s era recording of the story!).
The rabbits being gassed and buried alive in the flashback where Holly's warren is destroyed.
It was disturbing enough in prose, but Captain Holly's illustration of it... Not to mention the sight of one of the most likeable characters almost suffering one on some wire.
In the movie, there's Blackavar. He doesn't die in the book, but he tries to kill Woundwort himself and gets his throat ripped out absurdly quickly. The gagging noises he makes as Woundwort kills him doesn't help.
The blood coming from their mouths doesn't help.
And that poor cat in "The Terrible Hay-Making" (in the sequel.) It wasn't even interested in the rabbits!
Man oh MAN. You have no idea how gruesome and dark Richard Adams can be in his books. Many consider Watership Down to be among his more tame stories.
Many, many villains in the Redwall series. Deaths—shown "onscreen"—include being crushed under a giant bell, being pulled into a sinkhole and drowning, being devoured by a giant eagle, pierced through the heart by a huge crossbow bolt, and being slowly driven insane and to suicideby the heroes—and those are all in the first two books out of twenty-something!
Those were just the first two books in the series, by the way. Others include getting ripped apart by three snakes at once, sucked into a whirlpool, force drowned, and, also from the second book, being tossed into the air to land impaled on some upward-pointing javelins.
A fox got stabbed through the brain by the fangs of the wolf skull he wore as a helmet when he was picked up and slammed headfirst into a tree. Then Ungatt Trunn got possibly the most horrible death of the lot; he's left for dead on the seashore with a broken back, but he's still alive, and the tide is coming in veeeeeeerrrrrry slowly ...
There are also some undoubtedly painful deaths on the red shirts of either side. In one book, a shrew is shot in the eye with an arrow, in another a mook has his head and paw chopped off, and there are also many others.
In the first book was one villain murdered another by stepping on his throat, and holding his foot there until death.
Similar to Redwall but much, much worse: the Deptford Mice series. For example, the scene in Thomas where the mice and rats are trapped in the hold of a ship during a storm and several are crushed by the improperly secured cargo, then when they finally escape there aren't enough lifebelts for them all. The series also features rampant cannibalism, necromancy, a villain becoming powerful enough to wipe out the sun and turn his victims into ice-powered zombies, and a poison which dissolves its victims into puddles of tar.
Any children's book where the first chapter of the second book details what happens to the first Big Bad's corpse is...pushing it.
There is quite a lot of this in the Warrior Cats series. To name a few, Swiftpaw was brutally mauled by a pack of dogs, Tigerstar is ripped open and bleeds to death nine times, and Mudclaw is crushed by a tree.
One noteworthy "throat-getting-torn-open" death would be Ashfur's, due to its use of Blood Is Squicker in Water, and just how creepy his lifeless body bobbing around in the water as if he was still alive is.
When Yellowfang poisons Brokenstar, not even the main character can bear to watch him writhe in agony, and has to leave. If something is too scary for these cats, it certainly isn't family friendly.
Another poisoning death. Honeyfern has a seizure as she dies.
Tigerstar torturing Lionblaze with visions of him killing Heatherpaw/tail in a series of extremely violent fashions. The only one we actually see is when he slices her throat open and blood pours out. The other dreams don't show him killing her, but show her mangled body and the messy results. You'll probably end up wondering how it is possible to spray so much blood everywhere...
More psychotic hallucinations: In Sunrise, Hollyleaf imagines a mouse as Leafpool, and proceeds to tear her to shreds in a fit of rage, the remains being described as a "red pulp".
And then there is Moonrise, which features an Ax-Crazy mountain lion who goes around slaughtering (and presumably eating) cats.
Pretty much everything about dogs in the series. As mentioned above Swiftpaw is slaughtered by a pack of dogs, and Brightheart loses an eye and half her face to the same dogs (she doesn't die, though). Later in the same book Tigerstar murders Brindleface in order to use her body as bait for the dogs. Then there are the dogs in Sunrise, who killed (and presumably ate) at least six cats, and apparently tore one of them to pieces.
Whitestorm. Apparently he was covered in so much of his own blood, Firestar couldn't even tell what colour his fur was.
Rippletail has his shoulder pretty much torn open by a beaver's teeth, and then spends about an hour bleeding to death.
And who could forget Silverstream dying due to complications while giving birth, leaving Cinderpelt with complexes regarding the fact that she thought she could've saved her.
Tigerstar rips some cat's spine out.
The Alex Rider series, despite being a kid's series, has had some very graphic and almost cringe-worthy deaths. Some of these include being stung to death by a Portugese man-o-war, being blown up in a helicopter by a flying snowmobile, being impaled by a set of underwater spikes, having their back broken by a large magnet because of all the metal in their body and then drowning because of the weight, being crushed in a giant bottle with FREAKING QUARTERS, getting sucked into the engine of Air Force One with the remains being described as a "cloud of red gas", being sent back to Earth from space after being hit with a giant fireball, being crushed by a falling hot air balloon platform, having a hole blown in their chest by a medallion made of caesium while showering, having the top half of their plane fall on them before it explodes, and the most out there death of them all, when Kaspar is suspended in zero gravity, helpless as he floats backwards into a zero-g floating knife which impales him through the back of his head. Anthony Horowitz is one sick individual.
The main villain of Snakehead, meanwhile, is killed by having every bone in his body smashed to bits by the vibrations of a bomb going off underwater as he's riding a jetski. The result is described as still looking like a human for roughly half a second before collapsing into an unrecognizable heap of skin and gore.
The first chapter for the next book, Crocodile Tears, is now on the site. In that alone, a devastating nuclear disaster is set off. We hear what happens to those in the room the first explosion is triggered. Graphically. The first chapter.
Need we mention the Big Bad of Scorpia Rising melting in a pile of salt?
Mortal Engines, SO MUCH. About a hundred named characters die over the course of the four books, and millions more in the background. Apart from several dozen shootings and stabbings, characters are also crushed underneath mobile cities, ripped apart by robotic birds, incinerated in burning airships... Basically, death tends to be extremely brutal, but mostly very quick.
One poor mook'' got his head bashed in with a typewriter. By one of the protagonists.'.
His Dark Materials has a couple. In the first book, one armored bear defeats another in single combat by ripping his jaw off, then tearing his throat open, slicing his ribcage in half, pulling out his still-steaming heart and devouring it before shouting "BEARS! WHO IS YOUR KING?". It's pretty intense. (The film adaptation toned this down quite a bit, but it was still surprisingly gruesome for a kids' movie.) The same armored bear, later on, discovers the corpse of his (human) friend, and eats it as a sign of respect.
Darren Shan's writing, as well. The Saga Of Darren Shan isn't too bad, the most unfriendly death is probably Darren's second death. Committing suicide by impaling himself with a knife, and then spending the next 20,000 years screaming in a lake full of other dead souls.
The first book of the Demonata has the protagonist walking in on his dead family. Yes, we don't see them dying, but the results... His mother has been bisected into front and back, his sister is currently a meat puppet for a demon with insects for hair. You can't blame the kid for going temporarily insane. The series goes From Bad to Worse from there.
The Shapeshifter (a book series for young people) has Catherine Reader being incinerated while screaming "Not me! Not like this!"
Let's not forget that she was incinerated by Mia. That's right, Mia.
The Gashleycrumb Tinies... that's all that needs to be said.
The Thief of Always is the closest thing to a children's book Clive Barker has written, (the protagonist is ten, there isn't any sexual content) but that doesn't stop the four minions of the Big Bad from having fairly graphic death scenes: while Mr Hood just gets sucked into a whirlpool, Marr melts into nothingness Wicked Witch of the West style, Carna... shatters into shards of bone (the book wasn't too clear), and Rictus gets decapitated rather brutally. Jive's is the worst, though- disintegrating into ashes doesn't sound much worse than the rest, but it appears that he is doing so from the inside (he starts by just coughing them up) and it takes up almost an entire chapter. He's alive and conscious until his body has completely turned into dust, so that right before he's totally finished he pleads for Mr Hood to help him.
They may be aimed at elementary school kids and early teenagers, but the Dear America series is chock full of Family-Unfriendly Death accurate to the time period of each book. For example, the death of the protagonist's love interest in the Titanic diary, and, more traumatically, the multiple deaths that occur along the journey of a girl taking a wagon train out west (including one death from being swept away while crossing a river, and one brutal Infant Immortality aversion when the protagonist mistakes hemlock for an edible root and feeds a bit to another young girl while preparing dinner).
So Far from Home, the one about Irish immigrant mill workers, includes the hair-caught-in-the-machinery scenario. It also has what may be an even darker touch than most of the onscreen deaths: after the diary itself ends (on the less-than-satisfying note of the protagonist going off to try to bail an unjustly accused friend out of jail with the money she'd been setting aside to bring her parents to America, until they died), there is, as usual, an epilogue telling what happened to the major characters. Usually this has the diary's author settling down with the hardest period of her life now behind her, having a family and living to a ripe old age, with a nice personalizing Call Back or two to some plan for the future she'd mentioned or something. In this one, she's bluntly said to have died of cholera at seventeen, just a couple of years after the book takes place.
Dying because your baby has broken your spine as it tries to get out of you is a bloody gruesome way to die. Of course, this being Twilight, Bella gets"better", but still!
Any death in The Last Black Cat by Eugene Trivizas. Let's see, we have cats being drowned in hot tar, cats having their tongues stuck to the pavement, and then have a stemaroller rolling towards them, cats being burnt alive, having their heads smashed in with clubs, being drowned in quicklime, and one is even stabbed with a knitting needle. A children's book, my arse!
The Skulduggery Pleasant series revels in this. Everything from people just sort of coming apart in water, to being ground to mush by Cthulhu Expys, to graphic descriptions of being eaten alive by zombies after slipping in the gore they left behind... for the record, the books mostly aim at the 9-13 age group.
The Beach Dogs by Andy Jennings is full of these. And cute little doggies as well! The ones that stand out are the litter of puppies and their mother who are burned to death and the dog who gets trappy inside a deep freezer and slowly succumbs to the cold. As well as this, there are various shootings, one dog getting hit by a car (complete with descriptions later in the book of the body in various stats of decay), and a puppy who dies of asthma.
The Magic School Bus book where the class travels to the dinosaur times had a rather graphic illustration of a carnivorous dinosaur tearing apart another dinosaur (while the kids are watching this, their only reactions are to spout out incredibly lame puns).
Clare Bell doesn't shy away from brutality in her Named series, but by far, the death that sticks in most readers' heads is Meoran's in Ratha's Creature. The description of him being burned alive after Ratha hits him with the burning branch she's carrying in her mouth is nightmare inducing, especially if one's first exposure to the story was the later CBS Story Break adaptation, in which she merely scares him into leaving the clan.
Hell, Ms. Gee's death too, which occurs shortly after Hannah's. She has her flesh stripped away by being drenched in gallons of dragon urine from the awakening Gawaine, to the point where there's nothing left but her skeleton - which then disintegrates.
Out of the Dust is a story aimed towards elementary school kids about a girl growing up in the dustbowl. The first third is pretty tame, albeit a tad mellow. This changes, however, when the protagonist, who herself is about nine or ten, watches her mother burn herself on kerosene after confusing it with water for Dad's coffee. Not only that, but the mother is pregnant, the daughter's hands are mutilated, AND THE MOTHER STILL GIVES BIRTH TO A WRITHING, HORRIFICALLY BURNED CHILD!!! All of this is described in graphic, visceral detail. The two don't die from the burn injuries or smoke inhalation, but rather from infection over the course of several days/weeks. Oh, and this is during the Dust Bowl, so it's very likely some of the dust swirling around them might have snuck its way underneath the mother and child's folds of charred, seared flesh!. The rest of the book focuses on the protagonist's grief and guilt regarding the death, so the book never once lets you forget just how horrific that one moment of insanity was.
Listing all of the gory and creepy deaths in Fablehaven would take all night, but the big standout is probably Naverog's death. He gets bitten in half. His lifeless torso stump slumps to the ground, right in front of one of the teenaged protagonists.
Where the Red Fern Grows is a popular book with fifth graders and early middle schoolers, some places even require you to read it. The book goes into graphic detail about hunting animals, a character dying, and later the two dogs dying.
Septimus Heap employs some decidedly family-unfriendly ways to die, of which DomDaniel melting down in a pool of slime or Merrin Meredith being reduced to a hollow skin are probably the worst.
The Fire-Us Trilogy kills off all the adults with a horrible, organ-boiling fever. This leaves their children to starve, be eaten by wild animals, drown in swimming pools...if that's not enough for you, desperate children put all these bodies to use. Then in the last book, the protagonists find out that The Path Of Inspiration has been burning alive all children born since the virus in their quest to find the new Messiah.
The Hunger Games is ripe with this. Not surprising considering how many children have died in Panem for entertainment over the past 75 years. How about being caught in a net and speared by a trident courtesy of a fourteen year-old? Or having an axe essentially boomeranged into your head? Or having a nest of vicious, highly venomous genetically engineered wasps dropped on you while you were sleeping? This happening with the whole world watching you doesn't make it better.
The pods in Mockingjay crank this tope up to eleven.
President Snow tries to inflict one of these on Katniss. By brainwashing the boy who loves her, and she's fallen love with in return, into wanting to kill her because he fears she will kill him. Imagine finally being reunited with someone you love and thinking your reunion is going to be super happy only to find that person's hands around your throat trying to strangle you.
In any work describing a Steel Mill, you are certain to have at least one worker falling into a blast furnace, open hearth furnace, crucible full of molten steel or having something large and heavy falling upon him from a height.