Little Sweetheart - Thelma is pretty much pure evil, tormenting adults and her only friend more and more as the movie goes on. Even her friend, Elizabeth, becomes pretty cruel for a bit, but ends up redeeming herself. It almost equals death, instead becoming life in the last few seconds.
Daredevil movie - Even after Matt is blinded, the kids still pick on him. Although to be fair, before Matt agrees to fight them, they turn away, presumably to leave. They may have physically hurt him when he could see, but it seems like they weren't about to cross that line anymore.
Subverted and played straight in The Orphanage. Let's be mean to the deformed kid! Damn it, now we're ghosts. Let's try to help this lady find her missing son! Damn it, now they're both ghosts.
The protagonists in Drillbit Taylor are constantly menaced by two bullies, one of whom is completely psychopathic. Not only do they perform the normal bully tactics, but at one point the bullies chase the protagonists with a car, apparently in an attempt to murder them for trying to report their behavior. What makes this even worse is that most of this is done in plain sight of the rest of the kids in school and they do absolutely nothing about it, at least until the protagnists finally grow some backbone and kick some bully ass.
The flashbacks in Freddy's Dead: The Final Nightmare showed that it was, among other things, being relentlessly bullied by other children that drove Freddy Krueger to become a killer. Pretty horribly, the kids were shown teasing him about how he was conceived when his mother was raped by mental patients ("Son of a hundred maniacs! Son of a hundred maniacs!")
Also revealed to be part of the inspiration for Jason Voorhees' rampages in Freddy vs. Jason. You'd think Freddy would have a little sympathy. Oh, wait, that's right, it's Freddy Krueger.
In the 2009 Star Trek, we discover that even Vulcan kids display this tendency towards Half-Human Hybrid Spock. Being Vulcans, they're quite stoic and formal about it.
Spock: "Have you prepared more insults for me today?" - Vulcan boy: "Affirmative."
This was actually established the TOS episode "Journey to Babel".
The 1993 movie The Good Son. Although, Macaulay Culkin's character is more than just cruel...
Used on a couple of occasions in Schindler's List, such as the little girl screaming "Goodbye, Jews!" as they're being rounded up, and the boy who grins and makes a throat-slitting gesture at the cattle cars heading towards the extermination camp.
The entire The Karate Kid series including the fourth one is filled with bullies that are mean to the point of over top idiocy; sometimes it's influenced by an adult who enforces this behavior. In the remake not only are they cruel but also racist.
As noted by That Guy In The Glasses, the original features a Jerk Jock, but possibly redeemable bully and his intense, sadistic mentor. The remake has an intense, sadistic bully and his Jerk Jock, but possibly redeemable mentor.
In Kung Fu Hustle, in a flashback to his childhood, the Anti-Hero protagonist attempted to protect a mute girl from a group of bullies who were ganging up on her. They then proceed to turn around and beat him up instead, and afterwards, they even pee on him. This is when the protagonist says he decided to turn to a life of crime.
Real Genius features a group of college students selected for early advancement due to their intelligence. Naturally, they tend to come from backgrounds where they were bullied for this. Mitch, the main protagonist, describes to his roommate Chris how he was once stuffed into a mailbox by the Jerk Jocks at his old school.
From Toy Story, we have Sid, Andy's next door neighbor, who decapitates his sister's dolls and crudely fixes them onto anything he finds. Oh yeah, he enjoys burning holes into toys and strapping them to rockets. Thankfully averted with Andy, who cares very much for his toys, even when he's a teenager and had outgrown, as shown in the third film.
Played straight again in Toy Story 3 with the daycare children, though excused in that they're too young to understand that some toys aren't designed for rough play.
The protagonist's little sister in Remember Me is frequently a victim of bullying, but she says she can handle it...until towards the end of the film, where one of the bullies invites her to a, chaperoned by her mother, birthday party. The sister is nervous to go, but assumes the girls just want to be friends now...and then later we see her tearfully begging her father over the phone to pick her up, her pigtails chopped off. Apparently the girls ganged up on her out of sight of the parents, held her down and cut her hair off, and then told the parents she did it to herself—and, as her father reluctantly admits, it was off school grounds, so nothing can be done about it. The girls still mock her for her attempt at a decent hairdo the next week (she was too traumatized to leave her room) at school, in front of the teacher. Luckily, even if the teacher did nothing, the girl's older brotherand fathercertainly did. In fact, when said brother was sent to jail for doing something about it, the father bailed him out and then told him that he threatened all the girls' fathers if they don't transfer them to other schools straight away.
Henry Bowers from IT. Not only is he cruel, he's also a psychopath, a racist, a sexist, and an all-around asshole. While he was bad enough as a kid, he eventually grows up into an even worse adult who tries to murder the protagonists on multiple occasions before finally getting his comeuppance.
The main plot of the WWE production That's What I Am, where a kid gets paired with a intelligent student who gets made fun of due to his tall, wiry frame, red hair and big ears. The kid gets to learn his qualities and experiences the prejudice he faces.
At the end of Tomboy, the protagonists friends force her to take off her shorts, and force a female friend to check her pants, so that they can see if she's really a girl. There have been cases of kids actually doing this to transgendered or gender-variant kids too.
Parodied in Step Brothers, where elementary schoolchildren attack Dale and Brennan and force them to eat dog poop. Dale and Brennan are at least 40 years old.
The movie Chrissa Stands Strong, where three girls constantly bully Chrissa and her friend Gwen. They threw away Chrissa's clothes, gave Gwen a deliberately bad haircut, and even caused Chrissa's brother to become seriously injured.
In RoboCop 2 not only is one of the villains of the film a child, but every kid who appears in the film is either a violent criminal (one scene involves a group of little leaguers mugging a man and beating him to death with their bats) or a foul-mouthed little brat who drops F-bombs so frequently that the cast of South Park would blush.