The Deadpan Snarker comes in many forms; it could be the non-action guy, the sidekick, the Weasel Mascot, and even the cat. This trope deals with snark coming from a little girl.
The humor here is that we don't usually think of an adorable little kid as being sarcastic, and this character type is both smart and perceptive, capable of pointing out exactly what other characters keep concealed - often their feelings for one another.
Expect her to be Wise Beyond Her Years. Compare The Snark Knight.
Morino Ichigo from Please Teacher! and Onegai Twins (much more so in Onegai Twins). She's actually quite a bit older than she appears, though.
Evangeline and to an extent, Yue Ayase from Mahou Sensei Negima!. Later, Chisame takes this role, thanks to some liberal use of age changing pills so she's a bespectacled (or not) 10 year old. Before her abuse of age pills she didn't fit the body type requirement.
Anya Alstreim from Code Geass. C.C.'s also a pretty good fit, not so much in the short or undeveloped part, but she does contrast child-like mannerisms (like playing with a stuffed animal) with being so snarky that Lelouch initially thinks of her as downright inhuman.
Momoka from Daa! Daa! Daa! is a three-year-old little girl whose first scene in the series has her berating the heroine, Miyu, for aiding global warming by not recycling. From the back of a tricycle. Her snarkiness only increases as the series goes on.
A Rare Male Example is Naota from FLCL. The light novel explicitly mentions that his body hasn't kept up with his mental maturity. In the anime, his pajamas don't even fit a 12-year-old girl. He overuses 'ore' to compensate.
Likewise, Jin in Kannagi has...let's call them 'body issues'. He acts older than he is, and a lot older than he looks.
Saki in Shikabane Hime. She has a habit of speaking aloud her contracted monk's inner thoughts.
Loco in MÄR. Her aloof, gloomy attitude is sort of justified because she's actually much older than she appears, a curse induced by her choice weapon keeps her adult self looking like a very coldhearted 10-year-old.
Felli Loss from Chrome Shelled Regios fits this rather well, with a bit of Emotionless Girl mixed in, which is promptly subverted in her introduction, where she is seen her screaming and shouting insults down one of the city's ventilation shafts to relieve some frustration.
Ironically, Shirley Temple becomes a bit of a Little Miss Snarker in the film Little Miss Marker, after hanging around the gangsters who've unofficially taken her in, after she was left with them by her suicidal father.
Deconstructed in the Modern Family episode "Fulgencio", when Cameron and Mitchell wonder if Lilly is becoming this as a result of overhearing their snarky remarks to each other. At the end it turns out she's picking it up from Claire, who drives her to dance classes.
Young Amelia Pond has her moments, both when she meets the Doctor as a child, and when we see flashbacks of her and Rory and Mels growing up.
Jenny Wren in Dickens'Our Mutual Friend. She has a good reason for being so jaded, since her father's irresponsibility and severe alcholism leave her, at the age of about thirteen, to be the responsible adult of the household.
Ivy aka The Archive from The Dresden Files makes an attempt at this on behalf of the incapacitated protagonist. He notes that she's not very good at it yet, but he gets choked up nonetheless.
While her childish curiousity or perceived psychological instability are the character traits usually played up in adaptations, Alice could be surprisingly sarcastic and was never one to suffer fools gladly.
Rachel from the Sword of Truth series. Has no problem calling out Chase when he complains about the poultice he's forced to apply by telling him that if he'd just listened to her in the first place, he probably wouldn't have been hurt by the Eldritch Abomination he was surprised by and he wouldn't have to take the burning medicine.
The Cadpig from "The Hundred and One Dalmations" and "The Starlight Barking" by Dodie Smith. Okay, so she's a puppy, but that just adds to the cuteness.
Shiori Momono in 11eyes, a returnee from Italy who spends most of her time reading. The other part of her time is spent berating Tadashi. Everyone berates Tadashi, but she does it in a manner that hits him where it hurts.
Shantotto is this in Dissidia: Final Fantasy. Technically she isn't a little girl, she's 35, but as a Tarutaru she's diminutive. And almost all of her battle quotes are insults, specially her greetings to the other characters:
Arguably Maggie as well, though Maggie is more so of the Silent Snarker variety.
Kimi Finster from Rugrats would eventually become this in All Grown Up!, contradictory to her lovable self in the original series (with the exception of the newspaper comic strips), more less towards her brother, Chuckie Finster (and sometimes the other "Rats") on separate occasions.
Gwen Tennyson from the original Ben 10, frequently.