All the fun of unplanned parenthood, with none of the bother of unprotected premarital sex!
So, you're a single thirtysomething with a few issues. You're a workaholic, or you're immature, irresponsible, or something like that. And on top of that, someone you know (your sister, your best friend, maybe an estranged ex-wife) has just died. Life couldn't possibly get any worse, right?
Wrong. The dead person had a kid, and for some reason, you're the only person who could possibly take them in now. Sucks, doesn't it? You have no experience with kids, and between that and whatever your other problems are, you're really not cut out to be a parent at all. So this is absolutely the last thing you need.
Or at least, that's how you feel at first. But actually, the parenthood that has been suddenly thrust upon you is a good thing. Apparently, having a kid to take care of is like therapy and a dating service rolled into one — by the end of The Movie (or series, or arc, or what have you), not only will you have learned how to be a good parent (with some hilarious mishaps along the way, most likely) and gotten over all of your issues, you'll have found a love interest too. Now the three of you can be a happy family unit together. Aww.
Frequently used in works starring aging or maturing performers who are seeking to soften their image, to play off of comedic dissonance, or simply because the performer involved wants to do something that is family oriented for a change.
Note: This can, but does not specifically, occur in Soviet Russia.
Promotion to Parent also forces maturity but often with the added toughness of the new "parent" being not much older than the kids.
A common result of Sink or Swim Fatherhood. Compare Babies Make Everything Better. See also Resentful Guardian.
This is the central premise of Aishiteruze Baby, where Kippei, a lazy high-school playboy is forced to take care of his five-year-old cousin after her mother/his aunt, Miyako, is widowed and almost crosses the Despair Event Horizon, thus leaving Yuzuyu in his care in a moment of mental/emotional stability.. The gusto in which he devotes himself to being a good "mother" to Yuzuyu and the speed in which he matures is amazing, as well as quite heartwarming.
In the Sahara Mizu manga My Girl, when the protagonist's high school girlfriend dies suddenly, he learns that the real reason she cut off contact with him years ago was to hide the fact that she was pregnant with his child. Said child is now five years old and, of course, has to come live with her father — who is a shy pushover with no idea how to be a parent.
In Bunny Drop, 30-year-old bachelor Daikichi Kawachi takes in six-year-old Rin (who happens to be his orphaned aunt, but never mind). From time to time as he learns about the mechanics of parenthood, he wonders just who is raising who.
The premise of the anime Daa! Daa! Daa! is two teenagers who barely know each other, who have to take care of a small baby they find. Of course, the baby is also an alien, but still...
In Magical Girl Lyrical Nanoha Striker Ssecond sound stage, Fate worries that her adoptive children, Erio and Caro, by insisting that they are fine at the moment, are hiding any true problems that they may have (while they don't want to worry her and wish to become a bit more independent). By the end, when they come to an understanding, Fate reflects on Lindy's advice to let your adoptive children raise you, and thinks that was the case when she was being raised by her and Precia (before the latter went insane).
In Sakende Yaruze!, Shino goes through this process when the 17 year old son he didn't know he had shows up on his doorstep. He moves past his first love (his son's now-deceased mother), gains some emotional maturity, and ends up with a Love Interest as well. However, unlike the happy family unit scenario mentioned above, his new relationship is what causes his son to then leave him and go back to living with his strict grandmother instead.
Downplayed in Happy Yarou Wedding. Taking care of the 5 year old Shouta definitely spurs on Yuuhi's emotional growth, but Todou's influence, both as a lover and a quasi-father figure, plays an equal role.
In Papa no Iukoto o Kikinasai!, The 19 year-old Yuuta ends up raising his three nieces when his sister and her husband disappear while on a trip. His dedicates his life to taking care of the three girls and matures considerably as a person. This specific trope is dropped at least once a volume in the novels.
Rather the point of Otaku No Musume San. Kouta is a rather immature otaku until his daughter, of whom he had no prior knowledge, drops into his life. Not only taking care of her, but also trying to earn her love and respect forces him to grow the hell up.
In Little House with an Orange Roof, Shoutarou is given sole custody of his sons when his wife divorces him. He quickly learns how unprepared he is to be a real parent, though he gets better over time.
Ryuuji from Toradora! learned to be self-sufficient and how to cook, clean and sew since his father died when he was young and his Woman Child mother works late at night and sleeps most of the day, leaving him to do the household chores.
In Ouran High School Host Club Haruhi Fujioka is like this. Because of her mother Kotoko's death and her father Ryouji/Ranka's long work hours, Haruhi does most of the work at home, cleaning and cooking for Ryouji and otherwise trying to take care of him, even telling him not to overwork himself for her.
In Naruto after Tsunade's boyfriend dies, she takes in Shizune, his little sister that he was taking care of. However, since she spends all her time drinking and gambling, Shizune spends more time looking after her.
In Dragon Ball Z Piccolo becomes something more than the reincarnation of his sire's hatred while training Gohan.
In Marvel Comics' Crisis CrossoverInferno, a homeless drifter finds a baby that has been orphaned by the demonic invasion. Despite himself, he begins shedding his drunken bum self-image in an effort to protect the child. By the end of the comic, he's all but unofficially adopted the kid.
The furry comicCircles has a case of this, where the son was raised until his mid-teens by his mother, then his aunt and uncles when she was killed in a car wreck. The reason the father didn't get custody earlier was because he's gay. Oh, and living with five other gay men, only one of which he's in a relationship with. So far, the kid's doing all right, as are his "new" parents.
Northstar, in one issue of Alpha Flight, 'adopted' a foundling. It died of AIDS by the end of the issue.
Huey, Louie and Dewey were supposed to stay with their uncle, Donald Duck, only until their dad returned from the hospital (the triplets themselves are responsible for that, by the way). Neither father nor mother are ever referenced again, though, and they have lived with their Unca Donald since then. Good for him, as they save Don from life-threatening situations in a current basis, showing a superior intelligence and maturity level over him. That's not to say Donald hasn't gained any growth from entering paternity; as hilariously dysfunctional as their relationship may be, he effectively serves as the boys' daddy, raising them with his very low income and sincerely wanting the kids to have the best future possible.
Three Men And A Baby is a variant where no parental death is involved, just a "runaway mother" approach.
The Ur Example: Baby Boom. The baby was left behind by a very distant, European relative that the protagonist hardly even remembered.
Jack And Sarah, starring Richard E. Grant. Which contains possibly one of the cutest things ever committed to film, in which Grant (stuck with the baby after his wife suffers Death by Childbirth) carries the baby in a jiffy envelope with a sock on her head as a hat...
The sock-on-head bit is copied by Clive Owen in Shoot 'em Up. In his case, the newborn belongs to a woman he's never met before, who suffered Death After Childbirth By Shooting, and he's only looking after it because the Big Bad wants to shoot the baby too. It's that sort of movie.
In Discworld, this seems to have happened to Death, who adopted his daughter, Ysabell, after reaping the souls of her deceased parents. This first-hand interaction with a mortal child (and later Ysabell's daughter, Susan) is presumably a part of why he's developed such a fondness (and attempt to imitate) humanity.
Discussed in The Dresden Files; when Harry ends up taking Molly Carpenter as his apprentice in order to save her life, Michael says it will be good for both of them, because being responsible for someone forces you to become a stronger, more patient, more caring person. Unusually for this trope, however, Harry was by no means an irresponsible person before, (being one of the best examples of Chronic Hero Syndrome you could hope for,) he just becomes even stronger with Molly as a Morality Chain of sorts to help him deal with the stresses of his terrible life without snapping.
Kevin Hill - A short-lived series about a swinging bachelor and top notch lawyer, suddenly forced to care for his dead cousin's ten month old daughter, Sarah. The show's core centered around Kevin dealing with being a new parent and lawyer at a new smaller firm. The series had a definite Downer Ending when the show canceled in just one season with Kevin losing the baby to her remarried biological mother in court. The series would have continued after that point but did not gain sufficient ratings to be renewed.
Happens to Shane in season 4 of The L Word. Her deadbeat father's run off with another woman, and her junkie stepmother blames Shane and ditches Shane's baby brother on Shane's doorstep. Shane reluctantly takes responsibility, and having to be a stable parent for him is doing her a power of good and forcing her to give up her bad habits, and they're really bonding and becoming close — and then her father shows up and takes him back. * sniff*
Star Trek: Deep Space Nine: "The Begotten", where Odo takes care of an infant changeling. It dies, but in its short time restores his shapeshifting abilities and reconciles him with his father figure.
An older form of this with Rory pretty much guiding the kitchen and relationship-clumsy Lorelai Gilmore through life in the first four seasons on Gilmore Girls before Executive Meddling and Flanderization kicked in to turn Rory into every other TV teen.
The premise of Raising Hope. As an added bonus, not only does the main character grow as a result as having to look after the tituler Hope, but his parents do too.
iCarly has a Played for Laughs version with older brother Spencer taking care of sister Carly as their father is on a very long military deployment and the mother is probably dead.
In Coupling with Steve, though it's his kid. He's spent the entire series as a card-carrying Man Child, but his newborn son opens his eyes and stares in Steve's, "and I became a completely different person." And then the series instantly ends.
A heartbreaking example in AIR, where the Hard-Drinking Party Girl mother (actually an aunt) purposely acts irresponsibly and unparentlike because the kid is cursed to become physically ill whenever she loves and is loved in return, whether it be familial, friendship or romantic love, and also because she didn't want to get too attached to her out of fear that her father would one day come to take her away. Haruko only realizes that she was wrong and begins to act like a mother when Misuzu gets sick anyway, from befriending and falling in love with Yukito.
Subverted in Transformers Animated, where the Autobots don't think twice about taking Sari in. This is probably before they realize that eight-year-olds aren't user friendly.
In Time Squad, Larry and Tuddrussel have enough problems working with each other and doing their job, due to a complete lack of knowledge about history... Until they meet Otto Osworth, an orphaned 8-year-old history buff, who they illegally take into the squad (not without hesitation at first). Otto gains a better life, while Larry and Tuddrussel now have someone to keep them from killing each other; their Like an Old Married Couple dynamic also quickly makes them become like a mother and father to Otto, respectively.
Jackie Chan Adventures lampshaded this when it had Jackie admit this when Jade's parents complement him on taking care of Jade.
Sylvester the Cat in a couple of classic Warner Bros. cartoons would would tell his son it was time to discuss the facts of life, to which Sylvester Jr. would reply "Sure thing, pop. What do you want to know?"
This happens a lot with rock stars and their children. One notable example would be Marlon Richards, son of Keith.