Bravestarr: "The Price". Your friend or son could get caught up in the drug scene and die from the effects.
The Dexter's Laboratory episode "Misplaced in Space" has Dexter trapped in an alien prison where nobody speaks his language and he has no idea how to get home.
Madeline may have Tasted Like Diabetes at times, but the movie Madeline: Lost in Paris made great use of this when Madeline is supposedly adopted by a man claiming to be her uncle, only for it to turn out that he's a serial kidnapper, has kidnapped multiple girls this same way, and now all of them are forced to do hard labor in a lace factory—and one is horribly ill. Child labor is/was extremely common, and the idea of someone claiming to be family taking away one's child never to be seen again hit waaaay too close to home for many parents. The original book was about the title character almost dying of appendicitis, however, which many would find even worse.
Rugrats almost deserves a category to itself, as the titular babies repeatedly wander off and go on adventures while their inattentive, some would say neglectful, parents are none the wiser. The Darker and Edgierfilm is probably the biggest example, as the babies get lost in a forest full of escaped monkeys and a super-persistent wolf.
Episode "Home Sweet Homediddly-Dum-Doodily", where due to several misunderstandings, child welfare accused Homer and Marge of negligence and their children are taken away from them. It was particularly heartbreaking when Homer and Marge wander in their house to each of their kids' empty bedrooms. And when Marge and Homer heard Bart's signature ring, they rushed down to the front door, faces joyful, only to see nobody was there.
There was the episode where Homer's mother Mona dies. Homer has been reunited with his mother for the first time in a while, after being abandoned by her again, and he's genuinely angry at that. So he tells her that he doesn't want to forgive her, and goes away... only to find, later that night when he comes down to apologize to her, that poor Mona died in her sleep. For many adults, the realization that they are highly likely to see their parents die, and the idea of a parent (or any loved one really) dying after an argument is... sobering.
In "Mobile Homer", when Homer purchasing an RV causes yet another strain to his marriage with Marge. They have a big fight, after which Bart and Lisa take matters into their own hands by trying to return the RV themselves. Homer lampshades this when he and Marge find out: "It's every parent's worst nightmare: they've stolen a car and they're home alone!" Made even worse when the kids have trouble driving it, and accidentally drive off a cliff and land on a ship that's about to leave the country. Only some quick thinking by Marge saves them from being carried off.
The episode where Lisa finds a beached whale and tries desperately to save it hits us with the "not every life can be saved and parents can't solve everything" message, made even more painful by Lisa's Hope Spot dream where Bumbling Dad Homer of all people rescues the whale by organizing a ton of different people for the sole purpose of making Lisa happy
In "500 Keys", Maggie is locked alone in the car. She's smart enough to get out on her own, but it's still pretty scary.
Parodied when Lisa tricks Homer into letting her go downtown by herself on the bus. He casually tells Lenny and Carl this, and they're horrified. Cue Homer making up a story about how Lisa is so smart she overloaded a computer, which Lenny and Carl don't fall for, and Homer finally running off to save Lisa.
"Alone Again, Natura-Diddly" — Ned and Maude Flanders go to a racetrack and Maude, naturally offended by Homer's inevitable antics, gets up to go get her family some hot dogs. They look away, and Maude dies in a freak accident moments later.
"Bart vs. Thanksgiving" — Homer and Marge look back with regret when Bart runs away because of their rather harsh punishment of him. Topped off with Homer lamenting "Will we ever see him again?".
"The Call of the Simpsons" has Homer desperately searching for Bart after they both go over a waterfall. Thankfully, Bart turns up safe and sound.
In that same episode, Maggie runs into some bears in the woods and she is mistaken for one of their cubs.
Codename: Kids Next Door: Operation: W.H.I.T.E.H.O.U.S.E.. A young idealistic rebel wakes up one day and discovers that he has grown old and respectable and abandoned his ideals. His old comrades have become corrupt supporters of The Man, he is married to a shrew who used to be his girlfriend (though she was a shrew when she was his girlfriend so nothing changed there), his son despises him, his best friend has been driven insane by his betrayal and he is faced with the choice of crossing the Moral Event Horizon or be destroyed.
In the Ducktales episode "Nothing to Fear", Magica DeSpell used real-life images of Uncle Scrooge & co.'s worst fears to descend upon them. For Uncle Scrooge, this took the form of being told by Huey, Dewey and Louie that they secretly couldn't stand him and they only wanted his money, for HD&L it was that Uncle Scrooge never loved them.
The same episode also previously has Scrooge facing the fear of being penniless and having custody of the nephews removed from him as a result.
In the two-part pilot of Young Justice, the Justice League are angry that Robin, Aqualad and Kid Flash ran off on their own to investigate Cadmus without telling them. But when we find out that after capturing them, the Light's original plan was to clone them and send them off to the League as moles, killing off the originals, we can see why the League (particularly the mentors like Batman) acted the way they did. Then in the season 1 finale we find out this already happened to Green Arrow's sidekick Speedy. The "Roy" seen in the series is actually a clone of the original Roy created three years ago.
Then the guilt about it is compounded when Artemis fakes her death but everyone save Kid Flash, Nightwing and Aqualad are in the dark about it.
The Young Justice episode "Misplaced" explores the terror of parents being separated from their children on both sides. Sportsmaster deliberately invokes this by inciting a mob to lay siege to STAR labs on adult world accusing them of making their children vanish as a distraction to steal a piece of Starro. On kid world, there are a quite a few scenes of children being endangered by the sudden disappearance of their parents. Near the very end, Zatara is faced by a parent's ultimate nightmare: a powerful force kidnaps his daughter and refuses to let her go. Then Zatanna has to live with the fact that her father sacrificed himself to save her from her own decision.
Another chilling moment is explored from both ends. In one scene we see a baby boy trapped in a car wreck until Superboy rescues him. In another scene in adult dimension we see the boy's father wrecking his car in his panic over seeing his son vanishing before his eyes.
While the audience is aware in "Satisfaction" that Artemis is Faking the Dead, Paula Crock's situation is absolutely heartbreaking. It wasn't enough that she was disabled, spent time in prison (and thus has the record of being an ex-con), and couldn't stop her older daughter from entering a life of crime. No, she had to outlive her younger daughter too. No parent should have to visit their own child's grave.
Bart Allen/Impulse is practically a walking Adult Fear. Let's see. From a world where the Reach took over and enslaved humanity, likely is the only surviving member of his family and is WAY too happy-go-lucky because he's actually horrifically depressed. Brr...
EVERYTHING the Reach did and was planning to do their captives in "Darkest Before Dawn". Particularly the scene where they are shown electrocuting Beast Boy and Impulse. Also the discussion about how to "repair" the Scarab which would either mind-wipe Jamie or just brainwash him. Add in the discussion of how removing the Scarab would cripple him and then Impulse telling him about the future and scaring him. This fear is shown really well with Jamie's frantic "I'm still me!" after his fight with Black Beetle.
Aqualad's fakeFace-Heel Turn since mentors in Young Justice act as father figures whether they are legally the fathers of their sidekicks or not.
The Batman: The Animated Series episode "See No Evil" is about a woman dealing with her ex-con ex-husband who proceeds to befriend his daughter (who doesn't know it's her father due to his invisibility suit) and ends up kidnapping her.
Also, in Batman Beyond: Return of the Joker Tim is kidnapped and then completely destroyed by The Joker. And the damage remains for the rest of his life, turning a formerly idealistic and cheerful child into a very bitter and broken shell of an adult man. Again, NOOOOOOOOOO!
In Scooby-Doo! Mystery Incorporated, it turns out that Fred Jones Sr. kidnapped Fred as a child, taking him away from his real parents and feeding lie after lie to him, bringing the issue of parents not just lying to you, but not really owning you and treating you that way.
The first My Little Pony special involved a girl who couldn't be older than fourteen essentially being kidnapped by a talking pony and almost murdered. You wonder what her parents thought when she was gone.. The second special involved the antagonist nearly murdering a filly. To not say about the ponies losing their home and going through lotsa shit to recover it...
The series itself also had lots of this, since half the cast was made of fillies who are, for all effects, little girls. And they were in danger many, many times. Heck, one three-part story was all about one of the "girls" suddenly falling very seriously ill, her mother being super worried and unable to help, and their friends desperately struggling to find her a cure.
And in the series, the no-older-than-14 girl is joined by her brother and sister who are even younger than her. They also get into shit alongside the ponies and their big sis, including injuries and almost death.
An episode where Rarity has to spend a week with her much younger sister Sweetie Belle, with her essentially taking a parent role for in every scene they have together. They get on each other's nerves until they declare that they don't want to be sisters anymore, and Sweetie Belle runs away. Rarity soon has a My God, What Have I Done? moment and heads out to find her, and while the next scene has her doing just that, the fact that her epiphany happened in the daytime and the next scene is at night indicates that she's spent quite a long time desperately searching everywhere in town, worried about what might have happened to her baby sister.
Then there's season one episode "The Stare Master". The Cutie Mark Crusaders venture into the Everfree Forest, in the middle of the night, to find a missing chicken. Fluttershy, who was entrusted with their care, goes after them and bumps into a petrified Twilight Sparkle; she then realizes that a Cockatrice, a very dangerous chicken-shaped monster, is near...
The "Baby Cakes" episode featured a scene that's every parent's and babysitter's nightmare. Pinkie turns her back on the babies she's taking care of, and when she checks on them again, the babies have disappeared. To emphasize the Adult Fear, the following tense minutes where she's looking for them are even shot like something straight out of a horror movie.
"Dragon Quest" has Spike falling in with the wrong crowd. There's also a recurring theme of an adopted child rejecting his foster parents as not his "real" family.
Spike's not the only one to get a dose of this trope in the episode. He finally realizes that his fellow adolescent dragons are "the wrong crowd" when he finds out that they make a regular activity out of stealing phoenix eggs from their parents' nests and smashing them, purely because they find it fun. If that revelation doesn't push them over the Moral Event Horizon, their willingness to take the newborn babies after they hatch definitely does.
"The Cutie Pox" has Apple Bloom contracting a life-threatening illness with no known cure. Also, in the Cold Open, a throwaway Shout-Out to The Big Lebowski has Fridge Horror to the effect that polerasts (the equine equivalent of pederasts) are canon.
"Castle Mane-ia" has Fluttershy getting separated from Angel and going over all the terrible things that could happen to him in the castle. Then she watches a pillar fall on the silhouette of what she thinks is Angel (it's just two leaves and a rock)...
In My Little Pony Equestria Girls, Spike's kidnapping. From Twilight's perspective, that's her son / younger brother who just got snatched. She didn't know Sunset Shimmer wouldn't hurt him.
In the Darkwing Duck pilot episode, Darkwing gets captured by cops while Taurus Bulba kidnaps Gosalyn for the arming code he thinks she has. Seeing Darkwing helplessly screaming out her name is pretty chilling for a children's afternoon cartoon show.
Avatar: The Last Airbender features all sorts of adult fear: the danger of having your family die, the inescapable life of a refugee, inability to keep your loved ones safe....
...A foreign nation invading your homeland, an oppressive government controlling every facet of society, being rejected and betrayed by your loved ones, being forced to choose between your loved ones because they have taken up opposite sides of a conflict, and losing control of yourself and causing someone else to be hurt or killed. When Avatar plays for Emotional Torque, it plays for keeps.
Tenzin has his home invaded and his family attacked while he is going to work in the city. Then his family (including two daughters under 10 years old, a son under 5, and a minutes old newborn son) must flee their home from the attacking Equalists. And that all turns out to be in vain. Tenzin and his family end up captured by the Equalists and he and his children are going to be publicly stripped of their bending by Amon. You can see Tenzin's fear and helplessness as he looks at Jinora, Ikki and Mello, who are bound and gagged with him.
How about those Equalists? A group of extremists who are are willing to kidnap you, attack you, and deprive you of your abilities, whether you did anything to them or not. All that aside from trying to make enough money to support you and your orphaned sibling while working for a predatory agent who is clearly out to keep you under his thumb as long as possible. Or being press-ganged into going after the Equalists before you've even had a chance to finish your training, or finish growing up.
And from the Equalists' perspective: People of all sorts, from politicians to showmen to con artists to criminals might have superpowers that make them easily able to kill and subdue anyone who doesn't have those powers. Yeah, sure there are laws against it, but cremation is an easy way to dispose of a body...
Ikki disappears in "Civil Wars part 1" after Jinora and Meelo tease her, so Tenzin, Kya, and Bumi try to find her. But when nightfall comes...she's still missing.
"A New Spiritual Age" is even worse. Jinora watches as one of her spirit friends becomes corrupted and captures her, Korra is forced into a Sadistic Choice and when she wakes up back in the material world, Jinora's soul is still trapped in the spirit world. Tenzin perfectly exemplifies this trope when he asks Korra what happened to his little girl
In "Venom of the Red Lotus", for a brief moment it appears that Korra dies while in her despairing father's arms. The entire reason Tonraq agreed to seclude Korra in the White Lotus compound for most of her life was to protect her from the Red Lotus...and they apparently got her in the end anyway. Pouring salt in the wound, the guy responsible is nearby and laughs in triumph.
In "After All These Years", Tonraq finds out that Korra hadn't been with Tenzin for a while and only got letters from her. His daughter - heavily traumatized and still nowhere near her old fighting skills - has been missing without a trace for six months.
It has a major adult fear as Simon aka the Ice King's backstory: slowly and against your will going violently insane, driving loved ones away in fear and hate, aware the entire time of the slow degradation.
Season 4 in general. While the show in general is becoming darker as it progresses, Season 4 deals with Finn's changing perspective and feelings. There's something horrifying about watching him unable to process how he feels, as well as his rejections from various girls. Special mention goes to the episode "Hug Wolves", which is either about rape or sex; either way, it's about being unable to have a proper outlet for your pent up emotions and how it affects your relationships with those around you.
Lady Rainicorn almost being killed by Ricardio while pregnant. Knowing that she knows she's pregnant and just wanting to save the father of her child is a special adult fear, that not only will the person who she loves die, but also that they won't get to love their own children. The possibility that some, if not all, her children could now be miscarriages or deformed from being crushed in the knot.
The fantasy parallel dementia is later made worse (and more explicitly paralleling dementia) when later episodes ("I Remember You"/"Simon and Marcy") reveal that, in the wake of the apocalypse and growing ever more insane, the relevant person became a surrogate parent to someone suffering from Parental Neglect, only to eventually say something hurtful. By the present day, he's become a burden on the surrogate child, bothering and making life difficult and painful without a trace of memory as to the previous emotional relationship or awareness of what he's doing.
Played for Laughs in "Jake the Dad", where Jake and Lady Rainicorn have kids, and Jake starts worrying about them to the point of paranoia. His children are grown up by the end of the episode. In "One Last Job", Jake'd daughter, Jake Jr., is kidnapped and held hostage and Jake is told that his daughter will be let go only after he reunites with his old gang and commits a robbery with them. It turns out to be just a trick, though.
"Too Old" is chilling in its depictions of domestic violence and child abuse. Lemongrab hits, disfigures, starves, and eventually cannibalizes his partner, Lemongrab 2. Lemongrab abuses the lemon children as well, forcing them to carry out violent performances and depriving them of food. He reserved special hatred for Lemonhope, forcing the boy to live in the bathroom and destroying his musical instrument.
In "Nemesis", Peace Master is forced to surrender a duel with Peppermint Butler when he learns that his opponent has kidnapped his children and threatens to turn them into monsters. Even worse is that he DOES follow through on his threats when Peace Master refuses to stand down, mutating two of his three kids irreversibly. This is somewhat lessened by the fact that the kids think their new bodies are pretty cool, but from Peace Master's perspective he still saw this as his children being held hostage.
One episode of the cartoon featured monsters from The Realm kidnapping children on Earth by dragging them through portals under their beds. The episode opens up with a boy being taken while his father desperately and futilely tries to save him.
In another, Hank (who is 15 year old) is kidnapped alongside Bobby (as much 8). Then Venger blackmails Hank into betraying his friends (including Sheila, Bobby's 13-year-old sister) under the threat of torturing or killing Bobby. Considering that Hank is the Team Dad and often responsible for the team's safety, and that Sheila is a borderline mother figure to Bobby ever since being spirited away...
Last Illusion. Varla's Good Parents love her unconditionally even when she's the local Master of Illusion, but since Venger wants her and their neighbors fear her to death, they cannot do anything to save their poor 12-year-old daughter from him. Even worse, Varla's powers are such a strain on her that they're apparently killing her.
Another episode deals with the children being forced to experience their worst fears. Sheila's personal fear is incredibly relatable — being completely alone.
In "Phineas and Ferb Get Busted", Candace experiences this when she discovers that her brothers got sent to a Military School where they and many other children are being taught that imagination is wrong and tortured into slack-jawed obedience. Thank God that was All Just a Dream.
As goofy as it was, Street Sharks has the pretty freaky premise that at some point, your co-worker could turn on you, steal everything you've ever done, perform an extremely painful procedure on you, and turn the entire town against you, completely ruining your life. And when he's done with that, he'll do it to your kids.
In the episode "Crisscross", MECH and Airachnid find (and later kidnap) June through the internet. And how, precisely?
Silas: Ah, the mother lode.
Airachnid: Government database?
Silas: Social networking page.
At the beginning of the second season, June Darby has to let her son go on a mission of unknown length and danger in a former war zone, where the atmosphere itself is toxic. At the end of the second season, June sees the Autobot base get destroyed, without knowing that Jack and his friends had managed to escape. Though he survived, her son has to go into hiding from an army. Finally, June's entire town had to be evacuated because it is right next to the enemy stronghold, meaning that she can't even go home.
Angels Friends: When Kabiria and Urie get injured by creatures of limbo, Temptel is visibly frightened for them.
The Rocko's Modern Life episode "From Here to Maternity" has Filburt and Dr. Hutchison go through this when their egg is taken by Easter bunnies.
Parodied in the episode of Family Guy where Brian finds out that he has a 13-year-old (human) son. After hearing a news story, Brian has a rather over-the-top reaction to it, as he could not bear to think of his son in that situation. Peter and his friends find the reaction funny, and take advantage of the situation by asking Brian what he'd do if his son was in various dangerous situations.
LeonardoI did the best I could! There wasn't anymore I could have done!
Of course the one episode that reigns supreme is Same as it Never Was probably the most terrifying episode in the entire show showing how much of Crapsack World Earth would be if Shredder ever won, and there's the whole...Almost all the cast is killed right before our eyes thing.
Oh...And Donatello's secondary stage mutation in the Good Genes arch in the forth season, it's got to be pretty terrifying for someone you love to go mad and is slowly dying
The 2012 Teenage Mutant Ninja Turtles cartoon is much lighter then it's predecessor, yet somehow manages to have more adult fear then it did.
Splinter's backstory for starts in based on the idea that your best friend would suddenly turn on you and try to kill you and your family. Simply because he was in love with your wife and couldn't accept that she chose you.
The plot of New Friend old Enemy" is kicked off by Mikey befriending someone online, only to discover that he's really working for the Shredder.
In "Panic in the Sewers" Splinter begins to have nightmares about Shredder killing his sons.
In " I, Monster" The Rat King confronts Splinter with the fear that his sons would one day no longer need him and leave him.
In the first season finale Splinters discovers that Shredder has not only kidnapped his daughter after their battle fifteen years ago, he also raised her to hate him on the belief that Splinter killed her mother. When it was really the other way around.
And toward the end of the second season he finally gets her back, only for the Shredder to use her as a part of an elaborate trap for the Turtles, resulting in her getting mutated into a giant snake who nearly kills him. Needless to say it's painful for him.
This doesn't just apply to Splinter. Shredder is also angered deeply by this.
In Regular Show, a mother duck leaves her children alone for a few moments and comes back to find them gone. Mordecai and Rugby take care of the baby ducks for most of the day and the mother comes to pick them up after finding out where there are, only to find out that the babies have been kidnapped by a creepy old man. Fortunately, she gets them back by the end of the episode.
The Wild Thornberrys definitely has this. Eliza is able to speak every animal known on Earth. Yet, everywhere she and her family go, she usually winds up with a dangerous predator that could easily kill her if it weren't intrigued by her ability.
The movie adds onto this fear. Nigel and Marianne nearly have a heart attack when they see their daughter hanging off a rope ladder trying to save a cheetah cub from a poacher. This, along with the discovery of all of her adventures, results in them sending her away for her protection.
Akela, the mother cheetah, has to deal with this until the movie's end. She watched one of her cubs get taken away by man and was unable to stop him. After that, she has to sit and wait in hopes that her son will be returned safe and sound.
Due to being raised by a group of magical guardians, the titular character of Steven Universe is generally in some kind of danger, but the greatest example in the show so far is the episode "Steven the Sword Fighter", in which he finds himself alone in a dark house with an entity that intends to kill him. That same episode also has him witness Pearl "die" right in front of him.
Over the Garden Wall: This show is made of Adult Fear with the premise being two kids just wandering around aimlessly with no idea to get home, being pursed by an Eldritch Abomination who wants them simply because they're lost.