Lieselotte Achenbach from Arcana Heart. Wanted criminal in another dimension, and carries around a legless puppet with her sister's spirit trapped inside. And she's only ten years old. Nope... nothing creepy about that at all.
In Arx Fatalis, there is only one child in the only city explored in the game. There's nothing special about her appearance or clothes, but she has this soft-spoken voice which, when combined with outdated graphics (expressionless, pixelated facial features), simply makes your skin crawl.
The Little Sisters from BioShock are little girls of about five to six years' age who have been turned into living depositories for ADAM, the game's genetic Applied Phlebotinum. Their bodyguards, the hulking and homicidally protective Big Daddies, are scary enough, but a pallid little girl with a syringe on her arm who takes a childishly cavalier approach to sucking vital fluids out of dead bodies is on a whole 'nother level of horrifying. The worst part, though, is how lifelike they are if you stop to watch, especially considering that you're expected to kill their bodyguards for powerups and have the option to kill them for more.
Little Sister: Look, Mr. Bubbles, an angel! I can see light coming from his belly! Wait a minute... He's still breathing. It's all right. I know he'll be an angel soon...
Despite their creepy appearance and backstories though, their behaviour is somewhat the same as that of a normal child, taking into account their mental conditioning. The creep factor is significantly reduced for BioShock 2... because you're one of their bodyguards. Through his eyes, they're adorable.
Tiny Tina in Borderlands 2 is a 13-year-old girl who has some... interesting qualities to her character. When you're first introduced to her, you see her playing a more violent version of "Pop Goes the Weasel" with a bandit by blowing him up with explosives. She later on asks you to fetch a "friend" of hers, who turns out to be a baby version of the monstrous insects you fought in the region, in order to get ready for her tea party. She then asks you to fetch the guest of honor, who is a bandit named Flesh-Stick. She straps the bandit to a chair, has you smack him, and then tortures him to the point where the bandit begs for the pain to stop, only for Tiny Tina to respond by electrocuting him to death. Her demeanor throughout the whole game has her talking dirty as if she was 30-year-old while still doing little kid things like having tea parties, which adds to the weirdness factor. Considering that the world of Pandora isn't exactly friendly, the kid definitely went through some rough times to be what she is today. In fact, you find an audio log in the Wildlife Exploitation Preserve indicating that she was Forced to Watch her parents get tortured to death during Hyperion's slag experimentation, and was only able to escape with a hand grenade they helped her smuggle in.
Pale Luna from BoxxyQuest: The Gathering Storm is an emotionless little girl who can turn into an Eldritch Abomination through unknown means. She isn't evil though, and it's said that she sought the power in order to help her friends.
Gary from Bully is a tad old, but he fits pretty well in a more comedic sense. Sure, he's a sociopath, but he just loves being a sociopath so much that you can't help but laugh with him. Well, until he's caused the entire school to become a warzone and strips you of all your allies. Because A) he's crazy and B) he knows you're a threat. But still, he's so fun when off his medication.
Samantha Maxis from Call of Duty: Zombies. There's a reason she's called the Demonic Announcer, or according to Tank, "Devil-Voice!" Then there's her laugh when you get the Teddy Bear from the Mystery Box.
The killer from the Survival Horror game Camp Sunshine is in adult form in the main game, but in flashbacks you see parts of his childhood, where he was a very creepy child indeed. Somewhat subverted, though, as besides him being possessed by spirits beyond his control, he was actually a rather gentle child, even though he had a deformed appearance.
In Chrono Trigger, the young boy Janus and his cat Alfador are randomly encountered by the party in Enhasa. Upon meeting him as a stranger, Janus abruptly and unsettlingly prophesies, "The black wind howls. One of you will shortly perish." Later, Crono dies trying to protect his friends and Schala from Lavos, fulfilling Janus's prophecy. The creepy effect gets kicked up a notch if you realize that the black wind he mentions is actually the sound heard when traveling through time, and he grows up to be Magus, the primary antagonist until this point.
Clive Barker's Undying: All of the Covenant children once they were cursed. A particular mention goes to Lizbeth, who bit her nanny and licked her lips afterward.
The Child Crusaders. These creatures are the malevolent spirits of young children forced to march in a crusade, only to be horribly slaughtered. After the Breach is opened in that timeline, the evil of the Firstborn transforms the children's souls into vicious, hateful ghouls, harbouring great anger towards the adults who let them die. They appear as floating, sharp-toothed, pale-skinned creatures with their lower torso missing and their intestines hanging out. They also have no hands, and use the shredded tendons of their arms to attack. They also make very creepy moaning and shrieking sounds, and their disembodied crying can be heard before the Jericho Squad encounters them.
The form of the Firstborn could also qualify. Here you have an evil, all-powerful, godlike creature who despises humanity, and it takes the form of a small, naked child with glowing white eyes and a distorted voice made up of several male and female voices speaking at once.
Clock Tower: The First Fear has Bobby, a ten-year-old with giant scissors who chases the main character around trying to kill her. His face is grey and badly deformed. And there's also his giant, purple, severely deformed brother Dan.
The ghosts from Corpse Party. Specifically the Girl in Red, Sachiko Shinozaki, who murdered three other children in Heavenly Host and then let an innocent man take the fall. Their spirits were what created the spirit world of Heavenly Host and trapped many others there to be killed as well. Not to mention the reveal of Sachiko as the murderer is through the eyes of one of her victims... and you realize that she's giggling and essentially experimenting on each victim to see what stabbing them in what place will do. Sachiko is the definition of Creepy Child.
While most of the children in Danganronpa Another Episode: Ultra Despair Girls qualify, Monaca really takes the cake, and not because of any supernatural influence. All she wants to do is create the successor to Junko Enoshima, and although her original plan doesn't work, she still succeeds in the end.
Dante's Inferno has the Unbaptized Babies, who also qualify as Undead Children. They move like real toddlers, as a toddler was brought in specifically to do motion capture for them.
Deltarune: Rudy remarks that Kris used to be "the creepy kid next door," but is now "the creepy kid right in front of me." Although it's clearly just a friendly joke, Kris clearly has a reputation for creepiness in general, to the point where nobody even seems to notice that they've been possessed by the player. In fact, the end of Chapter 1 shows them breaking free of the player's control and proceeding to begin lurching around like a zombie, before pulling out a knife and smiling at the camera, revealing their eyes to be solid red. At the start of Chapter 2 we see the aftermath of the cutscene... they ate all the pie despite their mother explicitly asking them not to do that. This implies that their creepiness is harmless, though Chapter 2's ending subverts this again with them slashing the car's tires and then opening a Dark Fountain.
Nearly every child in Dragon Age is creepy, though in a couple of cases one suspects the creepiness was unintentional.
There's a creepy child standing around reciting a creepy poem in a Creepy Monotone in the Haven graveyard.
There's a villager's daughter in danger of Demonic Possession in a basement in Honnleath.
Arl Eamon's son Connor, who is possessed, is as creepy as they come. Although if the player saves him he grows out of it by the time of Dragon Age: Inquisition.
And then there are the singing ghost children in the Alienage orphanage ("But I'm dying, Ser Willem, Ser Willem, in pain").
Sally from DragonFable. She's a cute little six-year-old with blond pigtails... and she plays with the ears, eyes and hearts of zombies. For fun. After the boss is destroyed in the Necropolis Quest, Sally finds the now-abandoned subterranean university-city of necromancers, death knights, and the undead, and claims it as her playhouse. She even creates a cross between a Skeleton and a gingerbread man for the main character to try out for fun. Meet the Gingerdead Man.
The Elder Scrolls V: Skyrim has Babette, a member of the Dark Brotherhood who is actually a 300-year-old vampire who uses her looks to lull targets into a false sense of security.
The banshee from Fable II attacks by sending "ankle-biters", shadow monsters that look like creepy children with swords and knives, after you.
Sally from the "Mothership Zeta" add-on. She's a young alien captive who has been held in since before the nuclear war. She crawls around the air vents giving you information and opening doors for you. She knows way too much, and you can see her One-Winged Angel form coming from a mile away... except it never comes. She doesn't even try to backstab you, she is a fully dedicated ally. That said, she also seems very nonchalant about the very evident death of her family and most of the world.
Betty from the "Tranquility Lane" quest. She's the avatar of the sinister Stanislaus Braun in a twisted simulation of the 50s-esque world of pre-war 2077, who has spent decades torturing, tormenting, and toying with the other inhabitants.
The Fatal Frame series has many examples, one of them being Ayako from Fatal Frame: Mask of the Lunar Eclipse. She's as cute as a button, but there's a very good reason she was in that mental institution.
Alma Wade isn't the villain of a video game named F.E.A.R. for nothing. Every single time she appears is so creepy that it'll make you scream and jump. And you can't shoot her, since she's a ghost. And it gets worse when she grows up...
Bahamut's Fayth from Final Fantasy X. It's just... the mysterious way he speaks to Tidus, the fact that his eyes are always covered, the fact that he's one of the few characters in the game who actually understand everything, the fact of how incredibly creepy his version of the praying song sounds, due to him being such a small child, the fact that his battle-form is a giant, civilization-obliterating dragon-something-hybrid-beast... This child must've given some people serious nightmares.
In Fire Emblem Heroes, the Big Bad of the game is a very creepy-looking Little Miss Badass named Princess Veronica, who summons heroes and villains to fight the protagonists Alfonse and Sharena. She's all but stated to be more of a deeply-wounded Dark Magical Girl, however.
The title character and protagonist of Fran Bow acts as a decidedly non-villainous example. She's not evil, but some of her actions and observations are just unnerving. Other child characters in the mental institution where the game starts are the same.
The character simply called "the boy" in the Gadget series. This perpetually expressionless child appears at the start of the game to switch briefcases with the player character and frequently reappears for the rest of the story, where he's shown to be able to appear and disappear anywhere and float through the air. Some characters who have been exposed to the brainwashing machine "Sensorama" have also seen the boy, calling into question if he's even real or if he's just an illusion. Only two entries in the Gadget series offer some definitive explanation for what he is: the spin-off novel The Third Force, which has him be a part of the series' Applied Phlebotinum, Xenium, taking on a human-shaped form, and Invention, Travel, and Adventure, which alternatively reveals that he's actually your handler, Theodore Slowslop, secretly watching over you to make sure you complete your objective.
Kamila in Ghost Trick acts like a wholesome, happy little girl until she's possessed by Yomiel and smacks Lynne around with an uzi. Even her character sprite is different, with her hair down to hide her eyes in shadow.
One of these follows you around, going by the name of Wild Flower. Although her actions and attitudes aren't creepy per se, one has to wonder what the design team was smoking when they designed her. The fact that she's the already-dead host of Spirit Guardian Chai Ka and his "Other" certainly doesn't help matters any either.
That game also features a pair of ghostly children who drowned during the flooding of Old Tien's Landing. One of them tries to convince you to help her get revenge on the orphan master who left them to die.
Nugget from Kindergarten is mostly just a relatively benign Cloudcuckoolander, but he has his moments. He has the protagonist poison the resident Barbaric Bully to death for throwing food at Nugget during lunch, has dug a hole in the sandbox so deep that you'll die if you jump into it without the proper precautions, and he knowingly summons the apocalypse in the secret endings for both the first and second games.
The King of Fighters: Kula Diamond starts as a very creepy and sheltered pre-teen girl who nonetheless has a good heart underneath all the snow and ice powers, but barely knows how the real world works due to her upbringing as a guinea pig and assassin for NESTS. She gets better, but she still retains some traces of the trope.
Annie from League of Legends, in addition to looking rather creepy, can cast advanced magic and animate her toy bear to ravage enemies. Said murderous teddy bear is actually a real live demon bear that she's ensorcelled. His name is Tibbers.
The Legend of Zelda: Ocarina of Time has the little Kokiri girl you meet in The Lost Woods as an adultnote a.k.a. Fado, the first of three characters to bear the name, right after the depressed mannote a.k.a. Grog disappears. It's her utter deadpan and the fact that we never do get any further explanation. It gets worse due to Fridge Horror. It's a Crapsack World post-Time Skip... and before the Time Skip, this girl was perfectly normal and one of your friends. What happened to turn a normal kid into this?
Girl: That guy isn't here anymore. Anybody who comes into the forest will be lost. Everybody will become a Stalfos. Everybody, Stalfos. So, he's not here anymore. Only his saw is left. Hee hee. [...] Heh heh heh. Are you going to be... too? Heh heh!
Some of the creepiest children in the series are the ones that are inside the moon from The Legend of Zelda: Majora's Mask, because they are wearing the masks of all the bosses you have killed. Especially the child wearing Majora's Mask, which is sitting all alone under a tree, staring into space. This is all completely unexplained. If you look closely while you're forking over your masks to them, you'll see that Link is backing away slightly each time. The questions they ask (recalling the story of the Skull Kid and the Four Giants) suggest that they're all part of the Skull Kid (Or more likely and much, much worse, Majora itself), and some of the lines they say are pretty unnerving too:
Twinmold Child: Heh, heh... Thanks... You're nice. Umm... Can I ask... a question? Your true face... What kind of... face is it? I wonder... The face under the mask... Is that... your true face? Majora Child:[right before you fight it] Do you want to play with me? OK, let's play good guys and bad guys... I'll be the good guy, and you be the bad guy...
The Moon Children all share a distinct semblance to the man who is easily the most terrifying and intimidating character in the whole series. Yes, that's right, it's The Happy Mask Salesman. Capable of changing position without ever moving, scary when he finds out you didn't get his mask, oh, and when you fail and the moon destroys all of Termina? He still comes after you.
The Legend of Zelda: Twilight Princess has Malo. Perhaps the reason he becomes an insanely successful business entrepreneur (before the age of 8, on top of that) is because everyone does what he tells them to just to get away from his blank, soulless expression. The fact that his voice almost sounds like that of a grown man really doesn't help.
The Legend of Zelda: Phantom Hourglass has the Cubus sisters, who look like little girls in hooded dresses and are scared of spiders... but are for some reason on an extremely creepy haunted ship. Their eyes (unlike Link and Linebeck) are black, with little dots of blue in the middle, and they seem extremely "off" until the player's suspicions are confirmed and they turn into ghastly grinning flying demons.
Little Nightmares: The main character of the game, Six, definitely qualifies. A tiny, malnourished girl in a yellow raincoat, she spends the game sneaking around the Maw, attempting to avoid being caught or eaten. Her hooded face and thin, pale form are unsettling enough, but then there's the subject of her eating habits...
Lucius of the game Lucius, who is essentially Damien Thorn in all but name.
Maze 5: Sinister Play has a foggy-eyed boy and girl in black Victorian clothing who Speak in Unison and have Reality Warper abilities.
Boy/Girl: Humans are mere puppets for us.
A unique example would be Ridley from Metroid: Other M, who first appears as an adorable, fluffy chicken-rabbit-thing. He is seen again, simply staring at Samus with the most frightening look ever. He is then seen once again after that growling and consuming a corpse, only stopping to hiss at Samus.
The Neverwinter Nights mod Bone Kenning: Art of the Thanaturge has Lina, a little girl on the second floor of the Kavesk ale hall who's the only unrelated person in the village who isn't afraid of your character. She casually mentions wanting to use a voodoo doll on her mother and is friends with a hobgoblin which can be summoned by reciting a rather... interesting rhyme:
Mother's hands at sunset To tuck us into bed Cobnell's hands at midnight And at cock-crow we're found dead
Nintendo Wars: From Advance Wars: Days of Ruin, we would like to introduce Penny, whose interests include explosions, and... actually, mostly just explosions. Don't worry, Penny likes you. Unfortunately, Penny has a tendency to do what Mr. Bear says, and Mr. Bear HATES YOU!
The titular OMORI is an eternally depressed child who usually sports an empty, hollow expression on his face, and when he doesn't, it's usually even worse◊. He is a Psycho Knife Nut and his skills include lovely abilities like freaking enemies out with his Thousand-Yard Stare and debuffing enemies by mocking or shunning them. To top it all off, he's actually a mental construct created by Sunny to help him escape his past trauma, and once repression is no longer enough, Omori has no problem stepping up his game.
We also have the verymentallyunstable Kurodōji, who always speaks in a hissing voice and cackles like a maniac as he chops up his enemies with his oversized Sinister Scythe. The few adorable moments he has just ain't enough to balance out the creepiness.
The arcade sleeper hit The Outfoxies features the playable Ice Climbers-esque siblings Danny and Demi. They giggle like small kids typically do when they run, even if they happen to be packing a machine gun or RPG at the time, and after they've murdered one of their fellow assassins the same giggling sample is played while one of them draws an indiscriminate green squiggly mark on the television set that displays their recently expired target. It's much creepier in context.
Overlord II's protagonist is the son of the Overlord of the previous game. The beginning of the game will have you playing him as a child. Naturally, he is mostly faceless and quite malicious, particularly towards the kids that bully him in the beginning. Contrary to other examples of this trope, he looks quite scary and is given the all-too-appropriate nickname of Witch-Boy. Considering that Overlord tends to parody fantasy tropes and etc., the rather Obviously Evil look the Overlad has is deliberate.
Pharos. Did we mention that he likes suddenly showing up in your room in the middle of the night? Because he does that. A lot. And the fact that he just wants to be best friends forever... isn't. Helping. In addition comes the fact that his Social Link is the Death Arcana, in a game in which Tarot Motifs are good clues to a character's nature.
Alice is a recurring character. She happens to be a Humanoid Abomination with the mind of a young child, massive magical powers, and a disturbing lack of understanding on why, exactly, she shouldn't kill/eat/drain to death/feed to the darkness/necromantically revive people who want to be her friends. She has a lot of magical potential and is not averse to invoking Night of the Living Mooks as a valid tactic. All this while still retaining her innocence and Lack of Empathy.
Phantasmat 5: Behind the Mask has Thomas, who wears a black Victorian boy's outfit, has a pale complexion and empty black eyes, and chants morbid rhymes in monotone.
Pity Party: The protagonist claims that nobody came to the party because everyone thinks she's weird. She spends the game staring silently at the camera while creepy events unfold, and reveals herself as a demon at the end.
In the Strange House in Pokémon Black 2 and White 2, a building where Ghost Pokémon reside, you also meet a ghost girl. You see her three times while exploring the place; the first two times, she mutters things about darkness and nightmares, and then vanishes. Then, when you find the Lunar Wing in one room, she talks to you, and asks you to give it to a Pokémon before disappearing. The Pokémon you must give it to is Cresselia, who is found on the Marvelous Bridge; if you want to capture it then, you are able to try. You might also see the ghost girl on the bridge, but she vanishes forever if you succeed in capturing Cresslia.
Allister in Shield version is a young Ghost type specialist with a quiet, Limp and Livid manner who's always hiding his face behind a creepy mask, which seems designed to resemble the ghost-type Galarian Corsola◊. He's actually very shy, non-malicious, and even a bit adorable, but he can still be eerie.
PARIAH from [PROTOTYPE]. And if the Web of Intrigue is anything to go by, he's eternally a child, and can kill anything by touching them.
Some of the kids from Psychonauts have creepy tendencies. This trope also comes into play when you talk to any camper who is missing their brain.
Milka uses her invisibility powers to spy on people.
Dogen is a friendly kid, but he is a little odd and has no problem blowing up a group of squirrels who he thinks are telling him that he'll kill everyone.
Crystal and Clem are peppy to the point of obnoxiousness, but they're sometimes seen doing uncharacteristically creepy things like mixing poison into drinks or standing on the roof, commenting on how the others will "be sorry". It's heavily implied the two are suicidal and were trying to kill themselves.
The Xenoas from Requiem: Bloodymares are essentially a race of Creepy Children... who were eventually made playable. Childlike bodies, with some creepy physical traits, adult-like intelligence, and a usually-hidden disdain and hatred for all other races.
The hero is routinely followed by a silent young boy and his apparent nanny. The boy stands silent with his creepy pallid skin, piercing gaze, and blonde locks, while his caregiver speaks for him. That ain't no child, but a powerful fallen angel trying to groom the hero to be a Messiah for all demonkind to lead them in their battle against God. Nothing too complicated, really.
Alice, the strangely out-of-place Alice Allusion who turns out to be one of the most terrifying spell casters in the game, capable of maxing out the magic stat with ease and casting the single most powerful dark-based 1-hit-kill spell possible.
Lymle of Star Ocean: The Last Hope. Mostly due to her Creepy Monotone and doll-like face. Although she has a good reason for being like this: She once accidentally sent herself to Hell with her symbology and it broke her completely.
The Narrator from the Starsiege cutscenes. The major cutscenes in the game are narrated by a young girl with a British accent and an oddly extensive vocabulary. The opening of the game introduces her with an oddly echoing humming and the beginning of a schoolyard chant, followed by her singing: "Little Lord Peter, missing his liter while Hercy plays in the red. Down came the Glitches and burned us in ditches and we slept after eating our dead." Also, in one of the possible endings, she further narrates, "It was only a question of time before the Cybrids captured the last human survivors. Now, we're all being systematically eliminated."
Eresh of Suikoden V. Being a frail mage who is apparently old enough to have known Jeane (way, way, way) back in the day just isn't enough; she also has to talk about her body as "this shell", too.
The Infernas in The Suffering. In human form, they're an immortal trio of eerie, smiling children that talk quite candidly about how they play with the souls of your dead children for all eternity. In monster form, they're charred corpses that giggle constantly as they soar towards you on a jetstream of fire.
Super Mario Bros.: Jojora from Mario & Luigi: Superstar Saga, a magical, levitating girl. She appears when you first enter Joke's End amidst some extremely creepy music and starts to taunt you. After a couple of more sightings, she says she's bringing a friend over to play... who turns out to be a hulk many times larger than she is, and the two attack you.
Soon after you finish the second mission in Survival Crisis Z, you have a vision of a greenskinned girl wandering down a bloodstained hallway. This is probably meant to be the first clue that this isn't your typical Zombie Apocalypse. They appear for real in Episode 3. And they have knives.
Tales Series: You only see him in a single brief flashback, but from Nephry's descriptions, Jade Curtiss from Tales of the Abyss was definitely creepy when he was younger. Apparently he liked to experiment on small animals. And himself. Frequently. Much more obvious in The Anime of the Game, in which he is terrifying.
The Keepers are a secret order of mysterious men and women who gather in dark places wearing black cloaks with hoods, so it is no surprise that the girl who translates the mystic words of the seer is also creepy. In the ending of Deadly Shadows, she is revealed to be a monster that wears the skin of a girl it killed decades ago, and infiltrated the organization that worked to stop her.
Lauryl from Thief: Deadly Shadows. Incredibly creepy voice (being voiced by frickin' SHODAN helps) and prone to sending you jumping by butting in while you're almost cornered by the Body Horrors in her asylum "home". There's a also bottle of her still-warm blood in the cellar, despite the fact that she's been dead for years. Yet another reason why the Shalebridge Cradle is still probably the scariest level of all time. Oh, and she's on your side.
Flandre Scarlet is a 495-year-old vampire with the body and mind of a child, as well as mental and emotional insecurities (read as "insane") to boot, who has the ability to destroy whatever she wants by bringing its "Eye" into her hand and then clenching it into a fist...
Rumia normally wouldn't have classified for this trope, seeing as she's too moronically inept to be of any actual harm, but one must never forget that she is a maneatingyoukai.
Sayo Samonji from Touken Ranbu has an obsession with revenge that definitely makes him this. This is due to his Dark and Troubled Past, since (being the personification of a real sword) he was stolen, used by robbers and killers, and finally used in a bloody murder that was fueled by revenge.
Turovero: The Celestial Tower: On the tower's fourth floor, Leilia and Ruby come across a pale, traumatized little girl. While Ruby is initially suspicious of the girl, Leilia insists on helping her, both out of compassion and to keep her under watch until they determine her true motives. Turns out, their initial suspicions were spot on — the little girl is actually Mortia, a Guardian of Turovero who, along with her "big sister" Viveca, is trying to break the heroes' spirits and force them to leave the tower. To really cement her creepy status, her eyes turn pitch black just before her boss fight, and her weapons? Voodoo Doll-like effigies of the protagonists, which she can twist and tear to cause damage.
Chara is hinted to have been one when more is learned about them in the video tapes in the True Lab and from Asriel at the end of the True Pacifist route, where we learn about their hatred of humans and their Thanatos Gambit. Then at the end of the Genocide route, we get to meet Chara. While most characters' text appears with an "accent sound", Chara's is completely silent, and while smiling happily, they tell you that the purpose behind their reincarnation is power, just before destroying the world and only agreeing to restore it if you sell them your soul.
Asriel/Flowey counts for this trope as well. While Asriel is normally as sweet and friendly as a kid could be, an untold time spent without a soul and festering feelings of regret about having spared some humans' lives made him cruel and vindictive. The fact that the strongest words he ever uses are "idiot" and "stupid", as well as the motivation behind his antagonism being his inability to let go of his "best friend" Chara, ultimately make him still seem childish despite his frequent nightmarishness.
The notorious Children of Goldshire are a group of six children who live in an upstairs room in one of the houses in Goldshire (an otherwise peaceful, low-level human settlement). They sometimes make trips to nearby Stormwind, except that they always form a group shaped like a pentagram, and if you go upstairs to their room, the mellow tune suddenly gives way to ominous ambience. People have reported hearing strange voices in the room, and some players end up spooked to such a degree that they swear to never enter it again.
Pamela Redpath, a ghostly girl in Eastern Plaguelands, although she's a lot more depressing than creepy.
A non-human example: Wrathion, the purified black dragon. In the Mists of Pandaria era, he was two years old and already well-known for being manipulative, and had players murder his remaining family, including his father Deathwing. His human form was a short human male, who looked like he was in his early teens. His dragon form was a tiny baby blackwhelp... the kind players spent the entire game farming for mini pets.
Abby Lewis, a little girl wandering around a deserted village in the middle of a witch-hexed forest. She enlists your aid in gathering her toys for a "tea party", all the while being far too cheerful and upbeat for her spooky surroundings. Midway through the quest chain, she disappears as you start discovering the remains of the villagers, while hearing her voice making little rhymes about them. Finally the time comes for the tea party itself, which turns out to be a summoning ceremony for a creature you naturally have to fight off. Abby vanishes after that.
In the horrific vision of Stormwind, the player can find orphans standing over the corpse of their matron in a pentagram shape like the above-mentioned Goldshire children, playing hackeysack with her skull and speaking in creepy rhymes. The shadow around them and the fact that the various forces and abominations don't react to their presence at all suggests that their youth made them no challenge for N'Zoth to corrupt.
Albedo from Xenosaga was this when he was a kid. He was clingy towards his brothers, namely Rubedo, beat his other brothers up a lot note Though that was only because he thought they could regenerate like he could, and was overall just an incredibly creepy child... which only got worse when he came into contact with U-DO and went insane.
Yandere Simulator: Ayano was like this as a child, due to not feeling emotions. She learned how to fake emotions to avoid bullying and make her father (who was obviously upset that she took too much after her mother) happy, which, arguably, makes her creepier. This extends to high school, where she feels her first emotions upon meeting Senpai and embraces her Yandere heritage.
if you stop to watch, especially considering that you're expected to kill their bodyguards for powerups and have the option to kill them for more.Little Sister: Look, Mr. Bubbles, an angel! I can see light coming from his belly! Wait a minute... He's still breathing. It's all right. I know he'll be an angel soon...
