The Secret of Kells' third act. Because the young protagonist Brendan has once disobeyed his uncle's (the abbot of Kells) strict curfews, he locks him and another monk who helped Brendan in the scriptorium, i.e. to keep them out of reach of the invading northmen. In the ensuing slaughter, the abbot has a very sudden and positive character change when he is horrified to see all his schemes and preventive measures against an invasion going up in smoke. He himself is wounded repeatedly and badly, and passes out. The scriptorium is set on fire. Unbeknownst to him, Brendan and the other monk managed to escape beforehand. They, in return, see the abbot lying in the snow and leave him for dead. Now, Brendan believes the abbot, the only parent and relative he had ever known, is dead, while the abbot thinks that Brendan, his only surviving relative whose own life he risked to save him as a baby, has burned to death because he himself had locked him there in the first place. The movie ends very much with a very dark Bitter Sweet Ending as this misunderstanding is cleared up decades later. But still, the fears of an adult authority to fail in really really trying to protect his community and his nephew's life are fully and conveniently exploited in this film.
The Lion King has an exchange between Simba and Mufasa, in which the latter admits that despite looking like the most badass father in animation history, he was still scared beyond belief at the possibility losing his son to the hyenas.
A double dose of this is applied a few scenes later where Mufasa dies. Scar lures Mufasa out by telling him Simba has been caught in a large wildebeest stampede, preying on him via this trope alone with damn good reason for it. A minute or so later, right after Hope Spot no less, Mufasa is killed and Scar tells Simba, who's a cub mind you and has just seen his father plummet to his death that it was all his fault. Adult Fear was in full heart/gut wrenching and Tear Jerker effect for this entire scene for both father and son. One cannot help but unabashedly cry at this poignant scene.
Despicable Me: seeing your children, whether adopted or not, being kidnapped. It's also just as bad to see them returning back to the orphanage after bonding with them.
The baby Rapunzel was kidnapped from her parents' room where she should have been the safest. Making it worse is that her parents wake up just in time to see Gothel escaping out the window with their baby daughter.
She's routinely emotionally abused by the woman she was raised to think of as her mother, to the point at which setting foot outside of the tower once makes her briefly angst about how she's a terrible daughter. This is sadly not only a fear for adults, but "Mother Knows Best" is horrifically dark for an otherwise fairly cheerful, encouraging movie, if you consider that Gothel doesn't use magic to keep Rapunzel locked up. She preys on her innocence, affection and vulnerability, like a real-life abusive parent.
"Abi Sutherland: Plenty of Disney films have wicked stepmothers; they’re quite ordinary villains in the genre. They do things like banish the heroine to the kitchen or send her out into the forest to be murdered. There may be rags and neglect involved. But Tangleds Mother Gothel is much worse than that. She uses love like a poisoned apple or a witch’s curse, as a tool to achieve her own ends. And she’s clearly written by someone who knows, bone deep, how that works."
The scene where Gothel returns to the tower and finds that Rapunzel is missing is eerily similar to how any parent would freak out if their child disappeared without their knowledge and they don't know where their kid was, even though we know that Gothel is the Big Bad.
Where young boys were turned into donkeys, shipped off and forced into labor, the parents not knowing what happened to their sons and if they did find them, they wouldn't have recognized their own kid, seeing how they are now stuck as donkeys.
And a subtler example from the same includes the moment when Gepetto puts on his coat to go out in the pouring rain to look for Pinocchio who never returned home from school. Hearing the agony in his voice as he paces around his kitchen is enough to make parents whose children like to play hide-and-seek in department store racks flashback a little.
Gepetto: What could have happened to him? Where could he be at this hour? I better go out again and look for him...
King Triton had to deal with the aftermath of his youngest daughter Ariel running away after having a huge and violent argument with her. His words "What have I done?" certainly brings the trope home.
Even worse in hindsight. After the third movie of the series we're made aware that King Triton not only believes humans are a threat to mermaids and mermen, but he holds them responsible for the death of Ariel's mother: his own wife. And while he was just trying to keep his youngest daughter safe, he throw her in the hands of his worst enemy and the kind of people he despises most with a single stroke.
Ariel gets her own in The Little Mermaid II: Return to the Sea. After an argument she has with her daughter, Melody, Melody ends up running away. Ariel then regrets being so harsh on her and not telling her the truth about her merfolk heritage, so she has to turn back into a mermaid to find her.
Mulan's parents found out their daughter ran away to join the army. They are not able to save their child from the horrors of war and possible gruesome death, since any attempt would reveal her gender and sentence her to execution. The reason why Mulan ran away in the first place was save her father's life; he was too infirm to go to war and survive. Their fear would have been compounded with the most extreme guilt imaginable. Not helping that guilt is how Mulan had gotten into a brief argument with her dad right before deciding to run away.
The Incredibles: The entire freakin' movie was full to the brim with Adult Fear.
The scene where Elastigirl realizes that the missiles are going to hit the plane and she frantically yells into the radio "Abort! Abort! There are children aboard!" Then she runs back into the back of the plane last minute, fully prepared to die with her kids, like any mother would.
Mr. Incredible is lead to believe both his wife and children were actually killed during that same scene, not realizing they got out safely. His horrified expression, and the revenge he almost takes, say it all. This combines the classic "fear for child" with the less-commonly depicted "fear for spouse" variety. Brilliantly demonstrated by Mr Incredible's "not strong enough" comment near the end.
A deleted scene from the original version of the movie would fit. Syndrome (a minor villain and not the Big Bad) breaks into the Incredibles' home at the beginning and freezes them with a freeze ray. In the middle of taunting them, he hears young Violet crying down the hall. He proceeds to drag the two with him as he goes after their daughter.
Near the end of the movie, when Elastigirl and Mr. Incredible hear the babysitter's voicemail thanking them for calling a replacement sitter for Jack-Jack, Elastigirl frantically exclaims that she never called a replacement. It's a short moment, but no less terrifying for the parents in the audience.
Penny was kidnapped from the orphanage, taken to a dangerous swamp with two callous adults (even Snoops doesn't care much for her). She's clearly there against her will, and can't escape because well, it's a dangerous swamp, that and the alligators will catch her. Later on when she's in the pirate's cave, she's at risk of drowning or being sucked out to sea.
Down Under gives us Cody. While not suffering from Parental Abandonment, viciously deconstructs Free-Range Children when he manages to walk right on in to a poacher who kidnaps him with intents of finding an endangered eagle. Said Poacher Would Hurt a Child. What makes it even worse is that there is a scene where it shows Cody's house with his mother shouting, "Cody! Cody!"
In Hercules, Zeus and Hera awake from their room to find that their infant son was kidnapped. When they did find him, he was mortal and couldn't return to Olympus with them. So they could only watch as their son is raised by another couple - by this point though, this trope is thankfully averted, as Alcmene and Amphitrion were Good Parents (if they weren't, Zeus would have just killed them), thus Herc ended up being Happily Adopted.
The threat of Lilo being taken away from her older sister and caretaker Nani's side by social services casts a long shadow over the entire film. The moment when it actually happens is utterly horrific. Many a parent watching it in the theatres gripped the seats when Nani saw a fire truck and prayed, "Don't turn left" in the direction their house was.
She watches a giant alien kidnapping Lilo. When she asks the other aliens to help her get Lilo back, they're forced to tell her that there's no way that can happen. (Fortunately, Stitch convinces them otherwise)
Astro Boy (2009). Toby's death, leads to manic-depressive behavior by his father.
An American Tail is full of this, particularly after Fievel sneaks onto the deck of a ship in a raging storm and his father watches helplessly as he's washed overboard. The tragedy compounds throughout the film as Fievel and his family are constantly in the same place but keep just missing each other.
In the The Secret of NIMH, it's scary enough for the single mother Mrs. Brisby having to deal with her critically ill son, but during the climax when her children are stuck in their cement block house and it's sinking into the mud the fear is amped up ten-fold.
The kidnapping of the puppies in 101 Dalmatians was this for Pongo and Perdita, as well as their human masters Roger and Anita, who react as if their own children had been taken.
Maurice has to watch as Belle arranges to be kept prisoner in his stead, all while he cries for her to just escape and leave him to his fate. He spends the rest of the movie trying to rescue her.
Once Belle and Maurice are reunited? Belle faces the fear of having her father taken away from her, as Gaston blackmails her into either becoming his puppet-wife or getting him thrown in the local asylum. She takes a third option and proves her father is telling the truth... but they're imprisoned and the townspeople go Storming the Castle.
Tarzan plays on the same parental fear of losing a child as many of the other Disney movies listed here. A little before they find baby Tarzan, Kala and Kerchak lose track of their infant gorilla son in the jungle while the deadly Sabor is on the prowl. Unlike other Disney movies, the parents and child are never reunited since Sabor kills and eats the baby gorilla. With the added "bonus" of knowing Sabor was also able to get into the house Tarzan's parents made and kill them, then stuck around, probably intending to go after the child while he was alone. If Sabor had left, if Kala had not adopted him, Tarzan would almost certainly have starved to death in his crib.
How to Train Your Dragon has Stoick believing his son was dead after the fight with the Green Death. And this was due to Stoick's own misguided actions that led to the above event. His "I did this" was downright heartbreaking.
This is the parental fear scenario presented in Help! I'm a Fish. The character is babysitting their niece and nephew for the evening, with their son there as well, and they accidentally fall asleep. When they wake up, they find a darkened house, with all three kids gone. When the parents return, they all go down to the beach to search, and find one of the skates used by the kids with no sign of them...
In Finding Nemo, Marlin's happy future together with his beloved wife is all torn apart one day, when he can't protect them from a barracuda. Only Nemo survives, with a disability, just in case Marlin was going to be anything less than terribly protective. Terrified that Nemo will be hurt, Marlin almost smothers his son, which drives Nemo to rebel, telling his dad "I hate you" and then swimming out into open water — where a giant, horrible thing beyond comprehension takes Nemo away as Marlin watches.
Nemo screaming "Daddy! Help me!" as this is happening makes it a hundred times worse.
And then there's the scene directly after it, where Marlin is rushing around the ocean and trying to look above the surface to try and get any clue of where Nemo was taken, all the time yelling his name and growing more and more desperate.
The original Ice Age film is certainly more serious than the sequels. Manny's Troubled Back Story Flashback reveals that his family were killed by human hunters with him unable to protect them. The tigers attacked the human settlement in the beginning with the sole purpose of kidnapping and eating a baby. The baby's father tries to protect his family and fails, and is seen throughout the movie desperately trying to find them.
One happens right in the beginning of the movie. Fergus was having a nice picnic with his wife and small daughter when a bear comes out of nowhere and goes after his wife and daughter.
Where Merida runs into the forest after a fight with her mother. When she comes back, it was clear that Elinor had been scared and gone out to look for her.
It has a scene where Merida is trapped in a castle with Mor'du. This is horrific enough from her perspective, but watching from above is her mother, who is helpless to do anything as her daughter is pursued by a twelve-foot-tall bear intent on eating her alive.
Fergus finds Elinor's room trashed and her clothing torn, coming to the realization that a bear was there. Then he finds what is likely the same bear attacking his daughter. Fergus likely didn't come into her room, see that and think "A bear has attacked my wife". He would have come in, see the trashed bed and ripped clothes and think "Someone has attacked and raped my wife". Only after looking closer at the evidence would he realize it was a bear.
The moment Elinor realizes that she accidentally hurt Merida when her mind lapsed into acting like a real bear. And especially when she realizes she accidentally hurt her husband as well.
ParaNorman: Centuries ago, the town put an accused witch to death. The accused was an innocent little girl whose only "crime" was acting in a way they couldn't understand, since they assumed her natural born gift to see the dead was the result of witchcraft. In short she was accused of being a witch for talking to the only people in the entire town who didn't treat her like a freak. Not only was this sort over-reaction towards people who were "different" common in Real Life. The whole community is against them—they bully them, ostracize them, and perhaps someone decides to kill them... and there was nothing to do to save them. To make matters worse her family could never leave the town that killed her since they had to make a ritual in order to keep her vengeful ghost asleep so that she wouldn't take revenge or have to watch how the town twisted the story of her death into a tourist attraction. This means they had to watch it happen instead so they are not only unable to stop the defilement of her memory they know she may never be able to truly rest in peace because of what happened to her.
This comes up in both The Prince of Egypt and Joseph King Of Dreams. The first movie opens with the abduction and killing of the Jewish babies and, while the actual deaths aren't shown, we do see the Egyptian soldiers bringing weapons into homes and grabbing the kids, while the parents scream. Then, there's the part where Moses runs into the desert, while Ramses tries desperately to get him to go home. He never sees his parents again, and his brother was clearly worried about him when he came back. Finally, there's the killing of the Egyptian firstborns including Ramses's own son. The second movie is centered around the idea that your brothers can be jealous enough of you to sell you into slavery and lie about your fate to your parents. Joseph latter turns the tables on them by threatening to the same thing to Benjamin.
Joseph: But why? Why should you care if I lock him up, beat him, make him a slave?
In Wreck-It Ralph, King Candy tells Ralph that if Vanellope races and her glitching is seen by the players, the plug on their game may be pulled and Vanellope as a glitch cannot escape the game like the other characters, leaving her trapped inside the game. When the Cy-Bug invasion happens, Ralph panics that he will fail to get one little girl out of the game to save her from the gruesome death of being eaten alive.
In Rise of the Guardians, two children went out to ice skate and the brother (none other than Jack when he was a human) drowned to save his sister.
In Kung Fu Panda 2, Po discovers that he's adopted and spends most of the film fearing that his real parents abandoned him, a very real fear for anyone who's adopted.
The opening of Escape 2 Africa, the sequel to Madagascar. All of it. While his father Zuba is distracted for a minute, cub!Alex wanders off and is kidnapped by poachers. When Zuba realizes what's happened, he chases after the poachers' truck, desperately trying to save his son. Alex's crate is knocked off the truck and into the river, where it ends up floating to New York. Zuba, however, doesn't notice, and continues to chase the truck. Until a grown Alex winds up back in Africa and reunited with them, Zuba and his wife believed their son was dead. Zuba must have felt very guilty for all those years, thinking that it was his fault his child was dead because he failed to protect him.
The King and Queen of Arendelle in Frozen has one daughter born with ice/snow powers who could potentially harm people and accidentally does so to their other daughter. They are forced to isolate both sisters from each other and the outside world to protect them but their well-intentioned yet misguided attempts to help their daughters resulted in misunderstandings and trouble for them later on.