Alita: Battle Angel: Alita is a small, wide-eyed, sweet girl who loves chocolate. She is also a re-embodied Cyborg URM special forces soldier who underwent elite cyborg martial arts training who smashes and dismembers cyborgs many times her size.
Wesley Snipes from the Ugandan action film Bad Black is a cute little child who teaches the far older Ssali how to be a commando.
Zoe from Blade: Trinity. Despite being threatened/tempted by Dracula himself, she showed no fear, merely stating that she wasn't afraid to die because she was going to Heaven and said to Drake "My friends are coming to kill you.
Buffy the Vampire Slayer: Nicki manages to stake one vampire during the final battle (albeit while his back is turned) and punches another a couple of times, all the while looking out of place in her prom dress and uttering a girly exclamation of "Ew," after her most notable contribution to the fight.
Already mentioned in the literature section, but (because it bears repeating) Reepicheep from the The Chronicles of Narnia films. Modeled after Errol Flynn and voiced by Simon Pegg, Reepicheep goes mouse-to-man several times... and wins! Even though he is as cute as Lucy says (he prefers "courageous, courteous, or chivalrous"), he's a force to be reckoned with. He even tried to take on an army of Telmarines by himself! He easily manages to be the best part of both of his movies.
Cool World has Nails the Spider, especially when he psyches himself up to go and take down Holli without Frank's assistance. Him being voiced by Charlie Adler also helps.
The Dark Crystal: Kira's adorable and very resourceful, not to mention her beastmaster ability.
Phoebe from Ghostbusters: Afterlife - Tiny twelve year old little girl with a mop of curly black hair and oversized glasses. Picks up grandpa's old proton pack? Check. Completely unflappable when hanging out the side of Ecto-1's gunner seat with her brother driving at high speeds through town while shooting said pack at a ghost? Yup. And if that weren't enough, she definitely showed her stripes when she stared downGozer and distracted said entity with bad jokes. An entity that scared her grandpa past the capacity for rational thought, and this twelve year old kid is telling it jokes.
Tae-goo from The Good, The Bad, The Weird is such a wacky, klutzy, utterly adorable buffoon that you just wanna pinch those chubby cheeks of his... but don't, or he'll shoot you in the gut. He is, after all, the most fearsome criminal in all of Korea.
Gizmo in Gremlins 2: The New Batch becomes this after he grows too tired of the gremlins' abuse and decides to Take a Level in Badass and start acting like Rambo— that is, if Rambo was an adorable furry... thing.
The Pink Berets from Hop are a trio of cute bunnies with elite commando training. They're sent to retrieve the wayward E.B. from Los Angeles, using GPS tracking, ninja skills and Instant Sedation blowgun darts. Individually, they are Fluffy, Patches and Bit.
The Living Daylights: While the adorable and plucky Kara Milovy (Maryam d'Abo) isn't much of an Action Girl, she still charges head on on her horse to help Bond during the showdown on the Soviet airfield in Afghanistan, inspiring the Mujahideen to do the same, and she also drives a jeep under fire.
No Time to Die: CIA agent Paloma (Ana de Armas) has a kind, friendly, sweet-natured disposition, as well as a cute-and-cuddly appearance more befitting a fresh out of highschool Girl Next Door, and yet, when all chips are down, she is hands-down the deadliest lady in the film series since Wai-Ling of Tomorrow Never Dies.
Let Me In shows Abby, a 12 year old girl who is a vampire. She looks harmless, but she is strong enough to tear four teenagers to pieces in less than a minute. She proves it when exactly these teenagers want to drown or mutilate her boyfriend Owen.
Keanu from Keanu is an adorable, little kitten with big, black eyes...that's also able to karate chop guys 100x his size.
From Master and Commander, Midshipman Blakeney. He's this utterly adorable curly-haired twelve-year-old, who... gets his right arm amputatedbut doesn't let it slow him down, becomes something of a "fighting naturalist," and leads a group of men more than twice his age into battle, thus helping secure a decisive victory over the HMS Surprise's archenemy, the Acheron. His inspiration is Lord Nelson, also missing an arm.
Miss Meadows: Miss Meadows is quite pretty, quirkily sweet, and wears attractive if somewhat "vintage" clothing very well. She is also very handy with her concealed-carry-sized pistol.
Mako Mori in Pacific Rim, a cute Japanese survivor who wants nothing more than to have the heads of each and every Kaiju on a pike.
Detective Pikachu from Pokémon Detective Pikachu was this before his accident, being strong enough to defeat Charizard and scar its face. Not so much after his accident, where he lost both his memories and his power. He gets his powers back in the climax of the movie, hitting a Howard Clifford-controlled Mewtwo with a Volt Tackle strong enough to send him into a building.
Mathilda Lando from Luc Besson's The Professional is an assassin in training and the protege of Leon Montana. She also manages to carry out a few hits and even manages to sneak into a DEA building.
Sir Trenton from Racing Stripes is a horse that has no problem beating Stripes senseless before the big day, with the help of his army.
Shichiroji from Akira Kurosawa's Seven Samurai is short, chubby, jovial and can skewer you like a fish with his spear.
Kyle Reese (via Anton Yelchin) in Terminator Salvation. Moe with a shotgun. Also, his companion, Star: tiny, traumatized girl who knows how to crush a T-600 on Kyle's command? Nice.
Kate (Mary Elizabeth Winstead) from the prequel to The Thing (2011). Intelligence and bravery aside, she has been described by a review as "looking like a cute teenager trying to buy booze with a fake ID rather than an actual adult."
Bumblebee in the Transformers Film Series. Bright yellow, mentally younger than most of the other Autobots despite being physically around the same age, and over the course of the trilogy; racks up a Decepticon body count second only to Optimus Prime himself. In Transformers: Dark of the Moon, he even gets more weapons and armor to symbolize his evolution from guardian to full-fledged warrior. Yet, he still has his blue eyes and still talks through his radio; never once losing his connection with the younger audience of the movies.
True Lies: Helen, a sweet and dorky legal secretary, who through an impeccable combination of dumb luck, enthusiasm and thirst for adventure, becomes a butt-kicking adventurer worthy of her formidable husband, while still remaining a huggable sweetheart by the end of it all.
Wonder Woman is a kind, beautiful, warm-hearted and compassionate ray of sunshine who single-handedly sets out to fight World War One because she refuses to watch innocents suffer and die under the cruelty of tyrants, literally plowing through those who would victimize the weak like a hot knife (or sword) through butter.
from the The Chronicles of Narnia films. Modeled after Errol Flynn and voiced by Simon Pegg, Reepicheep goes mouse-to-man several times... and wins! Even though he is as cute as Lucy says (he prefers "courageous, courteous, or chivalrous"), he's a force to be reckoned with. He even tried to take on an army of Telmarines by himself! He easily manages to be the best part of both of his movies.