In Spy Boy, Alex wishes at the beginning for one to escape his crappy school life until he realize how brutal the espionage world really is.
Superman values both his Kryptonian heritage and his foster-parents. However, this perception varies from medium to medium or even from writer to writer. His origin doesn't fit this trope very well either way; in the Silver Age, he always knew he was Kryptonian due to super memory of his early years on Krypton. In the Post Crisis take, Superman didn't know he was Kryptonian until adulthood but it was evident long before then that he wasn't human (or at least, a normal human). In the latter version, he tends to cling to his human values and upbringing (especially in the Smallville series).
His twin sister Leia Organa as well, though she had a hard time accepting her biological father and always regarded herself as her adopted father's daughter.
Pan's Labyrinth. Although Ofelia rather loves her human mother, and seems to have loved her long-dead father, it's presented as an unambiguously better thing to live in the underworld full of magic. Mostly because dad is dead, mom is very weak-willed, and new stepdad is a zealous fascist. Unlike most examples, Guillermo del Toro actually takes into account the implications of such a statement.
In Wanted, the main character is bored and dissatisfied with his mundane life until he finds out that his father was a bad-ass super assassin and he's inherited his powers.
Who's Your Daddy?, about a boy who inherits his father's (played by Wayne Newton) porn empire.
The premise of The Princess Diaries. Subverted at first because Mia resists the idea of going from socially awkward, pathless San Francisco high schooler to ruler of a foreign country for most of the movie.
The Harry Potter series. Then again, both of Harry's parents are dead — and most of the other parental figures he acquires either abuse or betray him, or are killed. And the Dursleys who raised him get slightly sympathetic by the end. (Well, his aunt and cousin do anyways. The uncle stays a jerkass.)
This is the entire point of the new book series The 39 Clues in which two children find themselves to be heirs to the most powerful family on earth.
Kaye from Holly Black's Modern Tales of Faerie is a literal changeling, swapped as an infant for a human baby. She later meets the child she was switched with, who has aged only a few years in the Seelie Court.
Oliver Twist by Charles Dickens is a low-rent version, where the missing parent turns out to be middle-class — but given that the title character was thoroughly poverty-stricken, it's a major leg up.
In Eva Ibbotson's The Star of Kazan, the main character, Annika, a foundling, despite having a loving family, endlessly dreams of the rich woman who will sweep into the house one day and tearfully ask for the baby she abandoned in a church years ago. When such a woman really does appear, Annika finds that she does not like life as a noblewoman's daughter and, at the end of the book, is perfectly willing to accept that the woman is not her real mother, as expressed by her jumping off of a boat to get away from her.
In The Horse And His Boy, Shasta turns out, in the end, to be a prince. An unusual example in that The Reveal comes after the climax; he goes through the entire book believing himself to be a commoner. He does overhear at the beginning, though, that the man he thought was his father really found and adopted him, and he briefly fantasizes that he might be anyone, even royalty. Then he has to run away and seems to forget all about it.
Shasta is also an unusual example in that, although he's happy enough to learn that King Lune and Prince Corin are his father and brother, he's considerably less thrilled to discover that this means he'll have to be king someday. (His brother Corin is delighted to be shoved off the throne. "Princes have all the fun!")
In Andre Norton's Scarface, at the end, Captain Cheap reveals that he has his Revenge by Proxy: Justin Blade is the son of his old enemy Sir Robert Scarlett and will hang as a Pirate. Whereupon he learns that Justin's case had been remanded on new evidence even before they learned this.
Christopher Paolini's Eragon, which features the titular Farmboy becoming a Dragon Rider and leaving the village where he grew up with his adoptive parents. He knew they were not his real parents from the start, however, and didn't find out until much later on who his real father was.
In the sixth book of L. J. Smith's Nightworld series, Soulmate, Hannah learns that she is an olld soul, and emotionally related to Thierry.
Finding out the other parent is often a bad thing. For starters some parents were kind of absent. One can understand not telling a kid since they'd brag (Hey, it didn't turn out so well for poor Phaeton!) but when they need to know and they aren't there...well... Things are improving in the new saga, apparently. (demigods were claimed instantly; and they actually talk to their children)
The title character of Zilpha Keatley Snyder's book The Changeling spends almost the entire book trying to convince herself and a friend that she is just that.
Deconstructed in The Princess Diaries novels. A princess's duties and responsibilities are tough, and poor Mia didn't even want them in the first place.
In the Tunnels series, Will learns that he was adopted and that his real parents are inhabitants of the Colony, a secret civilization Beneath the Earth. Subverted, however, when his biological parents turn out to be just as unpleasant as his adoptive ones.
The Temeraire series has an odd take on this. While the titular dragon is considered a valued and unique piece of ordinance in the British Aerial Corps; when he goes to China he finds out that A) dragons in general are treated as large citizens/subjects with wings rather than talking warbeasts and B) he is by rights part of the Imperial Household. While he does return to Britain it is with plans for reform on his mind.
In Septimus Heap, Jenna, the only daughter of the Heap family, after ten years of living within the Heap family is revealed to be the daughter of the Queen and heir of the Castle. She had been adopted by the Heaps after the Queen was shot and Marcia Overstrand only barely managed to rescue Jenna from the Assassin sent out to kill them.
In Gene Stratton Porter's Her Father's Daughter, Linda knows her father is her father, but she seriously doubts that her sister is her sister. When she turns eighteen, she learns that her mother Died In Childbirth, and when her father remarried, he and his new wife had agreed to raise their children like actual sisters. (But it couldn't be hidden because it was In the Blood.)
The story of the Ugly Duckling.
In Gene Stratton Porter's Freckles, it's inverted; the hero is convinced that his birth is as lowly as it seems, and the other characters set out to persuade him otherwise.
Live Action TV
Emma's story in Once Upon a Time- she's found on the side of the road as a baby and grows up believing her parents abandoned her. In reality they're Snow White and Prince Charming who sacrificed themselves to send her to the real world and free her from the curse which is keeping them trapped in Storybrooke.
Connor, from Angel. The son of two vampires, he was abducted as a baby and raised in a Hell Dimension by a fanatical demon hunter, eventually returning to Earth as a teenager. His memories are later replaced with an elaborate web of fake ones, allowing him to live an ordinary teenage life, at least until a demon tied to his past comes looking for him.
Thankfully, he gets to keep his elaborate web of fake memories, so as not to go Ax Crazy.
Odo in Star Trek: Deep Space Nine discovered that he was actually a member of a dangerous race of shapeshifters who were also the leaders of The Dominion, the Big Bad of the series. Bonus points here, because his species was (due to their powers) actually called "changelings". This was presumably an intentional joke.
Subverted by the fact that it's evident from the beginning that Odo is from another species (its more the revelation of what place his species occupy in the Dominion that comes as the shock) and by the fact that Odo's adoptive culture is friendlier then his home culture.
The more regular explanation for the name "Changeling" is the Founders' ability to impersonate humanoids and use this for infiltration - that's what the Changelings did in legends (pretended to be human and corrupted others).
This was arch-villain Sylar's Start of Darkness on Heroes. It was further played with in Volume 3, with two wealthy Evil Geniuses each gaining his loyalty by claiming he really was adopted, and that they were his real parents. When he found out that it was all complete BS, he killed one and almost killed the other.
In Volume 4 they have Sylar's Changeling Fantasy actually turn out to be true, in that he really was adopted, and his biological father turns out to have been a powerful supervillain...but it's subverted as Sylar finds him a "big disappointment" due to all the Villain Decay his dad had undergone, courtesy of cancer, apparent poverty, and sheer boredom with life. Its implied as well that he never really did much with his abilities anyway other than kill people for their power and Sylars mom, and was just a self-centered Jerk Ass who doesn't give a crap about his son and never did. When he finds out Sylar has a Healing Factor and is effectively immortal, he tries to kill him for it and get a new lease on life. Except Sylar overpowers him without much effort.
Tin Man: DG is a waitress and part-time college student with little direction in life. She's plagued by a vague, unsettling feeling she doesn't belong in Kansas and strange, recurring dreams. Turns out she's princess of the O.Z., descended from and named for her ancestor Dorothy Gale, and the people she thinks are her parents are a pair of robots.
In Fringe, Peter is revealed to actually be the son of "Walternate" from the parallel universe.
Initially played straight, as Peter is happy to return home and reconnect with his real family. Later subverted as it becomes readily apparent that, due to losing his son to his doppleganger from a parallel universe, Walternate's sanity became even more damaged that his counterpart. Given how the latter spent 17 years in a mental insitution, that's saying a lot!
Myth And Legend
King Arthur is raised by Sir Ector. Though treated well, he's considered of lower rank than Ector's biological family, who have no idea of his true identity.
Takua from Bionicle was always thought to be a Fire-type Matoran, however, it is later revealed that he was a Matoran of Light, removed from his homeland and brainwashed into forgetting his past for his own protection.
The hero in Dragon Quest VIII was actually brainwashed so that he wouldn't remember that he's actually half Dragovian.
Inverted with Angelo and Marcello, though...
Cecil in Final Fantasy IV is adopted by the King of Baron. His mother was a normal human, of whom blissfully little is said, his dad was an alien from the moon. In a subversion. we later learn that his adoptive father-figure, the King of Baron, was not a human either, but the Eidolon Odin.
A similar tune with Terra in Final Fantasy VI except her dad was an Esper. She also wasn't so much adopted as "brainwashed" and mind controlled. For someone who spent most of her life that way, she takes it surprisingly well.
Played very darkly in the Kings Quest universe with both Alexander and Edgar. The Kings Quest Companion manages a partial Deconstruction by stating that Alexander doesn't even think of himself as a prince. Inwardly, he still thinks of himself as "Gwydion," Mannanan's former slave, and signs his name as Alexander-Gwydion.
World of Warcraft has Thrall, who eventually became the Warchief of the Horde and was the son of a shaman.
In Girl Genius Agatha doesn't know that she's the last in the line of a dynasty of Mad Scientists, or that her adoptive parents are their iconic assistants Punch and Judy (although she did know they were Frankenstein-esque "constructs"). She preferred her normal life. In a subversion of sorts, her mother is evil, and she has tried to possess Agatha, practically succeeding.
Also Gilgamesh, who believed himself to be an orphan taken into the Baron's care, and spent the first years of his life at the bottom of the pecking order established by the other kids on Castle Wulfenbach. He used to imagine who his parents might have been (maybe he was a lost Heterodyne!). After a couple of red herrings, he finally found out he was the heir to the Wulfenbach empire, raised in secret for his own protection. The revelation (and the need to keep it secret) leads to a wedge between him and his friends, especially his former best friend Tarvek.
Whateley Universe example: introverted Bill Wilson has no idea that he's about to manifest as a mutant, or that his parents are not only mutants themselves, but they work for the CIA as mutant superheroes. Or that his older brother and younger brother are actually mutants themselves (they don't know this yet either). This family is about to have a lot of 'splainin' to do.
In a nearly forgotten cartoon series called Wildfire, an 'ordinary American cowgirl' named Sara turns out to be the princess of a realm from which she was removed in infancy for her own safety. Later in the series she discovers that the man she lives with as her 'adopted' father is her true father the Prince, exiled for his own safety and brainwashed to forget his heritage, presumably to keep him from trying to return.
Don Bluth's Anastasia is a long-lost, amnesiac Russian princess. (With an interesting twist: prior to her discovery of her true heritage, she plans to pretend she's the princess and takes appropriate lessons in history and protocol. Then she's in for a surprise when the Big Bad, who swore to destroy the entire royal family, comes after her...)
In Hercules, instead of being a Zeus bastard like in the original myth, the title protagonist turn out to be his legitimate son, found later by his farmers foster parents.
Bleach has the protagonist grow up in a relatively normal, if somewhat wacky, household. Except for that whole "ability to perceive ghosts" thing. What Kurosaki Ichigo doesn't know is that his father is also a shinigami himself and has been so from the beginning. That raises a lot of questions about his true purpose and origins.
In Ashita no Nadja, Rosemary likes to think she'll somehow find herself in the middle of this. When her best friend Nadja is revealed to be a lost noblewoman... shesnaps. Big, BIGtime.
In Berserk, we meet a little girl named Rosine, a bright, imaginative child with a terrible home life. Her favorite fairy tale was about an a boy by the name of Pirkaf, who while loved by his parents never fit in amongst humans and eventually came believe he was a elf (due to being in similar appearance) and ran off to live with them. Believing the same about herself Rosine runs off as well but she obviously ignored the ending of the fairy tale. Pirkaf meets the Elves and learns that he is indeed human; his appearance was caused by the magic used to save him as infant thanks to his parents begging request for help. Upon hearing this Pirkaf runs back home only to find mysterious forest had sprung up overnight, caused by the Elves' anger over no one mentioning how they saved the boy's life, and Pirkaf— now completely alone— wept and wept.
In the end Rosline finds no Elves and falls in despair only made worse by being found by her abusive father who then starts beating the crap out of her at that moment her deepest despair activates a certain little egg. The summoned Godhand grants her wish to become an elf by transforming her into a fairy-like Apostle in exchange for both of her parents' lives. She has since taken to creating a "fairyland" where the children that she kidnaps are turned into her creepy little pseudo-elves in a very twisted version of the Changeling Fantasy, one that eventually comes crashing down when Guts comes calling.
Relena Darlian from Mobile Suit Gundam Wing learns early on that her birth parents were the rulers of a pacifist European nation, but it comes with a lot of "howevers". She didn't find out about this until her adoptive father was assassinated. Her adoptive family is very warm and loving, and they weren't boring by any stretch of the imagination (her father being an important diplomat who took her on business trips all over the planet). Also, her adoptive father was her birth father's right-hand man, and he was specifically asked to take Relena to safety as The Federation attacked their homeland. On top of all this, the "adoption" happened when Relena was two years old, meaning that while she loves her birth parents, she didn't really know them. As a result, while she reveres her birth parents as important people, she seems to love the Darlians more, and takes up their name once more in Endless Waltz.
Also parodied in Mark Millar's comic book mini-series Wanted, where the real family is evil and the "hero" decides he wants to become just like them.
Rather savagely parodied in The Sandman, in which a dream-avatar cuckoo sums up this trope with the line "Girls' fantasies are much simpler— their families aren't their families, their lives aren't their lives. Little cuckoos."
Subverted in Bone by Badass Grandma Rose Ben being a member of the young Thorn's real family as well. Thorn wasn't so much adopted as she was stolen away by her grandmother for her safety, who's just as much a hidden royal as Thorn is. As Thorn goes through the story and returns to her rightful position, Grandma Ben is right alongside her (for the most part), returning to her royal position also.
In the comic strip Zits, Jeremy's parents eventually revealed that they had been raising him in a dull middle-class existence when they were really dull middle class people.
In Suburban Glamour, the teenage protagonist learns that she's a literal changeling, and is the daughter of Fae royalty. She's initially elated to have the chance to get out of her dull, miserable life in a small middle-of-nowhere English village, but soon comes to realize that her Fae family are controlling and distant, and that they did abandon her for seventeen years without any explanation and as such have no right to barge into her life and start making demands of her. She decides to remain with her human parents, who at least love and respect her even if they don't always understand her.
The Doctor Who Magazine comic strip companion Izzy was adopted, and — having tension with her adoptive parents — often indulged in these kind of fantasies (which were often alluded to in the strip). By the end of her time with the Doctor, however, she'd adjusted to who she was and returned to her adoptive parents. The identity of her true parents was never revealed.
Inverted in Anthropology. A unicorn named Lyra is thrilled to discover she has human parents and gladly gives up her magic power and life in Equestria for a pair of glorious hands.
Subverted in the Belgian film Toto Le Héros, where this is a children's fantasies returning again to him on his senile dementia against his rich neighbor.
In David Lynch's The Elephant Man, the title character occasionally expresses a wish to find his real mother, on the hope that she could "love me as I am." What makes this so tragic is the subtle implication (which is historically true, by the way) that she clearly abandoned him for being ... well, you know.
There's a scene in Twins where Vincent mocks the idea of his origins.
The Shadow Over Innsmouth, by H. P. Lovecraft, features a young man who travels to New England to explore his genealogy and who ultimately learns that his great-grandmother was the queen of a race of amphibious fish-people, and that he is destined to eventually metamorphosize into a fish-person himself. But once you actually are a fish-person, you think it's awesome.
Tales of Innsmouth is a collection of stories by various authors, one of which raises the point that said fish-people will be Very Vengeful about their city being torpedoed thanks to his running to the authorities- the protagonist finds the perfectly preserved flayed skin of the original character. He is still alive as a skinless fish-man though.
In The Hunchback of Notre Dame, Quasimodo's birth parents are glamourous and exciting gypsies, but they abandoned him on the steps of a church, where Big Bad Archdeacon Claude Frollo — about 16 at the time — took him in out of kindness. Naturally, Disney couldn't cope with all this moral ambiguity, and in their version, Quasi's birth parents were very loving, and Frollo killed them, taking the child in out of guilt, and not even raising him himself.
It's implied that Quasi was traded for Esmeralda when she was just a baby and he was about 4 and was then taken by the church. His parents were such nice people, don't you think?
Subverted in the short story "Dragon's-Eyes," by Margaret Ronald.
In L. M. Montgomery's The Blue Castle, inverted in universe — Valancy's relatives explicitly talk about whether she is a changeling because of her sudden peculiar behavoir, and it gets shot down because of her age.
Harshly deconstructed in The Merchant Princes Series by Charles Stross. All the elements are there: Miriam Beckstein discovers she is the daughter of a powerful noble family with seemingly-magical powers from a medieval kingdom in another world, where she is engaged to marry a prince. But her family turns out to be an amoral organized-crime family that uses their magical powers for drug smuggling; the other world is by modern standards a squalid hellhole, where women have no rights; the prince is mentally retarded, and she is expected to marry him with no argument for the political advantage of her family, regardless of whether she wants to.
In The Bad Seed, Christine Penmark has always had this thought in the back of her mind that she was adopted, though unlike most examples of this trope, the idea fills her with horror. Her parents profusely deny this, and her friends assure her that this is a common childhood fantasy and no more. Unfortunately for her, it turns out that she was right, and her biological mother was a psychopathic serial killer... who may have passed on her murderous nature to Christine's daughter.
In Edgar Rice Burroughs's Son of Tarzan, the heroine Meriem is the kidnapped daughter of a French general, and reunited with her parents in the end after being raised by an Arab who kidnapped her out of Revenge.
Neal Stephenson's The Diamond Age is an interesting subversion. Nell is actually the biological child of Brad and Tequila, but over the course of the novel she comes to believe that her true mother is the woman who she can feel speaking to her through her Primer. And to some extent, she is correct: Miranda does behave far more like a parent to Nell than either Brad or Tequila, notably by sacrificing her own career and freedom to make sure Nell will be safe.
Subverted heavily in the Vorkosigan Saga, when Elena Bothari finally meets her mother. Turns out her mother wants nothing to do with her, because Elena is the product of rape. Then Elena's mother kills her father in revenge.
In the Bharaputra clone creche where Mark Vorkosigan grew up, the staff encourage their charges' changeling fantasies so that the clones don't try to fight or run when "Mummy" or "Daddy" comes to pick up his or her healthy new body.
In Evil Genius, by Catherine Jinks, Cadel Piggott (who knows he's adopted) learns that his father is Dr. Phineas Darkkon, who is, well, an Evil Genius. Subversion occurs when Cadel learns that his adoptive parents are actually in the employ of Darkkon, and deliberately cold so that Cadel would bond with his real father when they meet. Subverted some more when Thaddeus Roth, Cadel's therapist and Darkkon's right hand man, claims that HE is Cadel's real father.
The Roger Zelazny novel Changeling has its plot built on this trope. No, it is not the Trope Namer (see Changeling Tale). It's a subversion because Pol (né Daniel) acknowledges that the family that raised him was nothing but supportive, and openly admits that his real father was a terrible man when he went off the deep end, especially after learning more in Madwand.
Subverted in Coraline. The Other Mother is, in fact an evil faerie and the Other Father is a servant of said faerie. The other world is a horrible place to live. In the end Coraline is very happy to have her own parents back.
Inverted in Sharon Creech's The Wanderer: Sophie constantly thinks of her adopted family as her bioloical one, util she is finally forced to admit that she is adopted and that the sea (which she likes) killed her biological parents.
Live Action TV
Tossed, seemingly at random, into Quinn's backstory for the Sci Fi Channel seasons of Sliders.
Although, originally, this was planned to be a complicated ruse engineered by the Big Bads, that would be revealed at the end of the season.
Subverted in Kyle XY at the end of the first season where the main character supposedly found his real parents. In fact, Kyle was grown in a lab, the parents are actors, and Kyle goes along with the plan to protect his adoptive family, a situation which lasts a whole episode and then requires Kyle to make up another story for why he's returned.
In the episode "My Mother the Fiend," Veronica Mars finds out who Trina Echolls's real parents are. After the big reveal, Trina confides to Veronica that she had always dreamed that her real parents were movie stars. To which Veronica answers: "Trina, your parents were movie stars..."
One episode of Young Dracula revolves around Robin theorizing that he and Vlad could have been Switched at Birth (during a rather unlikely Branagh family holiday in Transylvania. Matters aren't helped when Ingrid then fakes a diary of her mother's to prove that this is the case.
Fringe's Peter Bishop was kidnapped by an alternate reality version of his father when he was seven. This (combined with the fact that crossing over permanently damaged the fabric of reality) kicked off Walternate'sStart of Darkness and attempts to destroy the other world. Needless to say, Peter had some issues with Walter after finding out.
Inverted by LOST: Alex learns she's not really the daughter of the leader of the Others, but that of a crazy woman who lives in the jungle. She's still happy about it, though.
The African dictator Jean-Bedel Bokassa tracked down his long-lost illegitimate daughter, who was living in poverty, and brought her back to live with him. Which makes the "evil real family" subversion an example of Truth in Television.
Opal Whiteley, or Princess Francoise Marie de Bourbon-Orleans (both names are engraved upon her tombstone), was a Teen Genius naturalist living in Oregon who kept a diary (now a respected classic) from the age of five or six. Stories about her life vary depending on who is telling them, but she seems to have believed almost from the beginning that she was adopted and was really the daughter of Prince Henri d'Orleans of France (himself a naturalist who wrote several books on geography). She later became a Cloud Cuckoolander and ended her days in a hospital for the insane.
Subverted by Calderon's Life is a Dream, where Segismund grows up in a prison, because it was prophesied that he would one day kill his father, the king. When he is reunited with his father and discovers that he's a prince, he's too angry to be overjoyed.
Alistair in Dragon Age: Origins, although he is well aware that he is actually a blood heir to the throne, he doesn't want it in the least bit, and actually treats this like this isn't really impressive. However he does know that he has a half-sister in Denerim, and when he meets her, she is almost enraged to see him (or even find out he still lives), and asks for money because she's not very wealthy (and has plenty of children) and Alistair is kinda...saddened more by finding out his half sister is incredibly rude than that he could actually become King of Ferelden.
Potentially a dangling plot thread when you consider that the father of Morrigan's baby can either be a male grey warden, meaning anyone from a city elf to a teyrn's son, Teyrn Loghain, or Alistair, who may potentially be king of Ferelden.
Flipped around around and inverted in Dragon Quest VIII. When Angelo's family died, he went off to the Abbey in hopes of having a place to live and at having a future, not having anything left to his name cept for a small sack, thanks to his dad being a bit reckless. The first person he meets at the Abbey who kindly greets him tells him it'd be his home from then on turns out to be his half brother, who was cast out and disinherited by said father because of Angelo's birth...and immediately tears into him, telling him to leave the abbey, accusing him of attempting to destroy his life there, and from then on, was never kind to him in the least bit.
Played oddly in Dragon Quest VII. The protagonist's foster mother actuall did give birth to the him; he was conceieved hundreds of years ago and gestated for seven months, at which point his real mother turned into a mermaid (thus lacking a womb) and the Spirit of Water teleported him into a random woman's womb at a random point in the future.
Squall Leonhart of Final Fantasy VIII turns out to be the son of the president of Esthar, the most technologically advanced and prosperous country on the planet. The game never actually shows Squall acknowledging this fact or expressing any thoughts about it, however; by the time it's possible for him to connect the dots, he's got more important things to worry about. Squall has also become pretty important on his own steam by that time, as the commander of a Magitek special combat force which is the only thing capable of saving the world.
Elisha of Gloria Union. Her real parents are Gariored and Enryetta, both of whom have great political and physical power. How exactly Zazarland came to raise her is unexplained.
Uncharted 3: Drake's Deception reveals that Nathan Drake is not a descendant of Francis Drake as he claims. As a child he was abandoned by his parents to an orphanage, where he became obsessed with Drake and took his name.
Direct inversion in Rêveillerie: Emelind is a literal changeling, but she considers the universe where she was raised to be her true home.
Well... more just an evil older brother. In the comics, we see a vision of Elyon's birth parents, who seem to have been good people before dying.
Disney's Hercules TV series had the lead's dull foster parents turn up to a parent evening, rather than his divine parents like he expected.
Rugrats, "Princess Angelica": Angelica convinces herself she's really a princess, and when the "Home Office King" comes to fix her mother's fax machine, stows away in his truck.
The Adventures of Sonic the Hedgehog had Tails adopted by a loving fox family who later turned out to be robots created by Dr. Robotnik to capture him. Sonic is completely unaware of the ruse, and spends most of the episode debating whether or not letting Tails go was the right thing to do.
Futurama: Leela, who only has one eye, believes she's an orphaned or abandoned alien, and dreams of meeting her species; later in the series, she discovers that her parents are mutants. Since mutants are second-class citizens relegated to the sewers, her parents figured their relatively normal-looking daughter would live a better life if everyone believed she was an alien.
In the BattleTech animated series, Franklin Sakamoto is kidnapped by his second-in-command, who had been secretly watching over him the whole time. It is revealed that Sakamoto was the illegitimate son of the Coordinator of the Draconis Combine. With the legitimate heir captured by the Clans, a group of hard-liners decide to use him as a figurehead, so they could remove the aging Takashi Kurita. Franklin escapes them, and in front of both the hardliners and the Combine agents sent to kill him, renounces his claim on the throne. Double-subverted in the game itself, as, after the events of the series, the Coordinator and his family accept him anyway.
Happens to Bloom, the protagonist of Winx Club: First she learns that she's a fairy, and then is revealed that her parents aren't her real parents, and that she's a princess of another world. It's partially averted, since Mike and Vanessa (Bloom's foster parents) are very loving, caring and supportive.
The Replacements: While Dick Daring and Agent K are not related to Todd and Riley by blood, they're a lot better than the orphanage they were living in before.
Skwisgaar Skwigelf convinces himself he's a god (or half-god; being very into Viking mythology to the point of swearing on the names of Odin, it may not make much difference) because he doesn't know who his mortal father is, and because his mother's neglect and promiscuity was what drove him into the snow, only to discover and subsequently learn to play the guitar he found in a cave. This may or may not be true; there's a theory amongst the fans that Dimneld Selftcark, Toki's guitar teacher, was Skwisgaar's biological father.
In the My Little Pony Tales episode "Princess Problems", Patch is suspected of being a long-lost princess, but the tomboyish Patch does not look forward to having to leave her friends and family behind for the life of royalty. Fortunately, it turns out Patch isn't the princess they were looking for.