Near the end of The Walking Dead season 4, unstable child Lizzie murdered her sister Mika, leading to one of the saddest ending scenes ever. It's no secret that horror movies and shows - and pop culture in general - tend to shy away from killing children. Even people who love gory horror can sometimes be turned off by the onscreen death of a child, and it's almost guaranteed to upset anyone who's already squeamish. It's just a natural gut reaction for most people, as a kid or kids being killed is one of the most upsetting outcomes one can imagine.
The aversion to depictions of child death in movies and TV shows is somewhat akin to the same aversion most people have to scenes of dogs or cats being killed, as kids and pets are usually seen as too innocent to ever deserve such a fate. That's actually what leads some horror writers to decide to kill off children in their narratives, as the general taboo surrounding it can get their work noticed, even if sometimes for negative reasons.
The Walking Dead has been surprisingly willing to kill off kids over the course of its ten seasons, even if minors are still more likely to survive than their adult counterparts. In the case of Lizzie Samuels and her sister Mika though, Walking Dead was able to pull off a one-two punch by making children both the killer and victim.
The Walking Dead: Why Lizzie Killed Mika In Season 4
Joining the cast of The Walking Dead in the first episode of season 4, Lizzie Samuels lived at the prison controlled by Rick Grimes' group, along with her father Ryan and younger sister Mika. Ryan ends up dying after being bitten by a walker, but with his last words, he asks Carol to look after his daughters, and for Lizzie to take care of Mika. One assumes he didn't mean that in the way Lizzie ended up carrying it out. Lizzie was shown to be a bit "off" from the beginning, especially concerning the walkers, who she believed spoke to her, and were intelligent like humans.
When this extended to Lizzie not wanting walkers to be killed, and seemingly thinking of them as friends, Carol became rightly concerned, and tried hard to make her see reason. Things continued to escalate, and despite showing flashes of understanding, Lizzie's attachment to the walkers continued. By the Walking Dead season 4 episode "The Grove," Lizzie lost it, stabbing her sister Mika to death, but not because she hated her. Instead, she thought Mika would rise as a friendly walker that proved they weren't different from humans. A horrified Carol and Tyreese find Lizzie standing above Mika's corpse, and things get worse when Lizzie says she was planning to kill baby Judith Grimes as well.
Faced with no other choice, as Lizzie was an imminent threat to anyone around her, Carol took her out into a field of flowers, and shot her in the back of the head. Despite it being hard to argue with Carol's logic, it's still heartbreaking, as Lizzie never did anything to deserve her illness, and at times, the normal girl that lived inside her would shine through. Once she made the decision to kill Mika though, it was clear her instability was too dangerous to deal with, especially during the apocalypse, where proper mental health treatment isn't really an option.