Children Forced to Kill

Having to kill another human being is traumatic enough. But when a child has to do it, either in defense of themselves, in defense of another, or being forced at gunpoint or swordpoint themselves to do it, the effect can be all the more horrifying. The fact that even children are forced to hand out violence in a setting to defend themselves adds to the cynicism of a setting. Children having to kill on a regular basis is a red flag for a Crapsack World.

The reasons for a child having to kill vary. They may have been attacked by someone and struck out in defence: they just happened to have the right thing on hand. Equally, they may manage to get the drop on someone who is trying to murder a parent or other carer. As mentioned before, they may be forced to do it, either as some form of Training From Hell or just from a complete sadist. This will be made all the more tragic if it was someone close to the character: a friend, relative or, worst of all, their own parent or even parents. If this is in a characters past, it will be a dark and troubled one.

Can lead to an even more warped form of Blood-Splattered Innocents. Often the cause of a Dark and Troubled Past. Child Soldiers must do this as a matter of course. Kid Hero stories with a particularly dark tone may also have this as normality for the setting, especially if that setting is a Teenage Wasteland. Tyke Bombs can become this if said Tyke bomb is forced to kill before it can be defused.

Of course, this goes along with Child Soldiers.

Note: Children who kill when they don't have to aren't this: that's some form of Enfant Terrible.

Anime and Manga

 * Black Lagoon: The Vampire Twins started out as this when they were forced to kill other children in paedophilic Snuff Films. At some point they broke and began to like it.
 * Happens in various Gundam franchises where the protagonists are young enough and the universe serious enough. Although combat is generally personified by mechas, the protagonists generally never forget that there is a person inside the war machine that is so easy to objectify, and spend time angsting over it.
 * In Gundam 00 the protagonist was brainwashed as a young child into becoming a member of a terrorist organisation. Part of the initiation involved killing his own parents.
 * Gunslinger Girl is all about this.
 * Madlax has this as part of the Backstory:.
 * Killua from Hunter X Hunter is an example. Being a member of a Big Screwed-Up Family of assassins, he's taught to kill from infancy, and forced into the life of an assassin without being given much of any choice in the matter. He was murdering people before he turned 6, and by the time he appears in the show - at an age of maybe 10 or 11 - he's already killed hundreds of people.
 * In D Gray Man, the average age for an Exorcist seems to be late teens. Allen's fifteenish when things start, Lenalee's about the same but has been working as one since childhood, Lavi's eighteen, and Kanda
 * Elfen Lied: The Diclonius are all young girls. The iconic bloody first episode shows Lucy kill scores of men, and she's in her early teens. Several other Diclonii are forced to deal lethal attacks to each other throughout the series.
 * Now and Then Here and There: Children are kidnapped from their home villages and forced to fight for the monstrously insane King Hamdo.
 * Trigun has this as  backstory. At a young age he kills  and soon gets adopted by an assassin, who teaches him the Bible, and how to kill.

Comic Books
""It's not the same as killing the dead ones…""
 * Cassandra Cain, the third Batgirl, was trained to be this when she was younger. Subverted in that, after her first kill, she panicked and ran off, vowing never to take another life.
 * In The Walking Dead,

Fanfic

 * In the Death Note Dark Kid Fic Shadow of the Valley Light forces his 12-year old daughter Hikari to follow in his footsteps.

Film

 * City of God has an infamous example in which a ganglord forces one small child to kill his even younger friend after they steal from him.
 * Likewise in Sin Nombre a gang leader forces a boy to kill a rival gang member held prisoner to be accepted into their gang. Said dead rival is then cut into pieces and fed to dogs.
 * The Quick and the Dead had Not forced to kill her father, but forced to take an action that took her father's life.
 * Full Metal Jacket.
 * Blood Diamond.

Literature

 * Ender's Game is the epitome of Children Forced to Kill. All of the characters are prepubescent or slightly older Child Soldiers being trained to kill an invading alien force.
 * Some beasts pulled into the fighting in the Redwall novels were quite young (as young as preteens - or younger). Some of whose reactions were understandable, while others were not.
 * H.H. Munro's The Easter Egg
 * Robert Muchamore's "Home" in which the protagonist is a very young guerilla soldier. After doing it he is nicknamed "Psycho".
 * Another Muchamore series has the protagonist (This time a very young super spy) shoot someone and require counseling afterward.
 * Basically the whole plot of The Hunger Games books.
 * The entire premise of Battle Royale is that a group of 64-ish students are taken to an island and forced to kill each other until only one survives. Adding to the "forced" aspect is the fact that they're wearing explosive collars and if no one dies for twenty four hours, the guys in charge will kill everyone...
 * The Tomorrow Series: Ellie and her friends didn't set out originally to be guerrillas...
 * In the Dark Disciple Trilogy this is the most terrible facet of the Children of Chemosh. This otherwise Nigh Invulnerable version of The Undead created by Chemosh can only be destroyed if a child strikes them. The destruction of the creature is so horrifying that it also traumatizes the child and robs them of their youthful innocence forever.
 * In A Song of Ice and Fire, nine-year old Arya Stark has to do this more than once when she's thrust into a wartorn countryside. She moves from simple self-defense to pre-meditated murder, and eventually.
 * Basically every one of the Animorphs at one time or another.

Live Action Television

 * The 24 Made for TV Movie Redemption included some children being trained to kill by the followers of an African general.
 * On Lost, Sayid got his start in murder by covering for his brother when forced to kill a chicken. Eko did the same thing, but with a person.
 * In Criminal Minds episode "North Mammon" an UnSub kidnaps three girls and imprisons them in his basement cellar, he will let two of them go if they kill one of them.
 * The guy in "Psychodrama" tried to force young boys to kill, or otherwise just attack, their mothers under threat of death.
 * It turns out that a young  killed his abusive father while he was threatening his mother.

Web Comics

 * Example from, of all places, El Goonish Shive. Well, depending on your definition of 'child', but  probably weren't much more than 12 when, during a class-trip to France, they wind up being targeted by a Somewhat Different Vampire. He's not technically human, but he LOOKS human - mostly - and while   does most of the fighting, it's   who ends up having to kill him - with an axe, even. Unsurprisingly, she was somewhat traumatized, and the recent arc that featured the flashback culminated in an Immortal decrying the irresponsibility of the two french Immortals who originally equipped   for the battle, while giving them no apparent alternative save dying at the hands of the vampire. Apparently, they could have simply informed the French Government's anti-supernatural-creature-squad instead, but elected to drag two pre-teens into a battle in order to 'recruit them for the fight against evil'. Omniscient Morality License, anyone?

Web Original

 * Survival of the Fittest: Even if you don't count the teenagers (who are usually 15-19) being forced to kill each other, there have been a few younger characters on the show as well, such as 12-year olds who did fit this.

Western Animation

 * Avatar: The Last Airbender is set in a world at war, and since the protagonists are children, it's only natural that this trope gets discussed. At one point we see a group of displaced children who are willing to kill innocent civilians for revenge against the Fire Nation, as well as the protagonists fighting (and almost certainly killing) soldiers right and left.
 * Aang, only 12 years old, absolutely hates this. He has nightmares about when his Avatar self went out-of-control, and is horrified at the thought of having to kill Fire Lord Ozai, as he believes all life is sacred.
 * Even Aang can be seen to kill at least inadvertently, if you pay attention. Do you think all those soldiers he buried in snow in "The Northern Air Temple" just dug themselves out and ran away? How about the Fire Nation sailors who were putting the Northern Water Tribe under siege? You can't blame all of their deaths on Koizilla. And then you have the buzzardwasp from "The Desert". Aang makes the thing fall out of the sky and hit the ground with an audible thud, and it doesn't move again. Of course, that last one was teasing at a Moral Event Horizon that didn't come to pass.
 * In The Venture Brothers, a clip from The Rusty Venture Show shows a young Rusty traumatically having to shoot a bad guy to save his father. Just one of the many little events that screwed up Rusty.
 * He also briefly mentions being forced to kill a man using a house key at age ten. Played for pitch-black laughs.