Siblings. Lots of us have 'em. Lots of us don't. The latter situation is often quite common in fiction, leading to a lot of only children running around.
But some fictional only kids (especially younger ones) are not happy with the situation. Maybe they're lonely because they have no one to play with. Maybe they're frustrated because they have no one to push around. Maybe they just see a lot of other kids with siblings in real life and are just envious. Whatever way, they know what they really want: A younger sibling, and they aren't afraid to ask their parents for one.
Their parents are generally less thrilled about this, because even if they also want another child, they're not keen on telling their kid where said baby is going to come from. Alternatively, if the parents are no longer able to conceive, they may decide to adopt to satisfy their child's request.
Frequently, kids will express a desire for a sibling the same gender as them: Girls generally want little sisters, and boys typically want little brothers. But the opposite situation isn't unknown: Sometimes boys want little sisters in an attempt to purposefully invoke Big Brother Instinct. Similarly, sometimes tomboyish girls will want brothers... and not-so-tomboyish ones want living dolls.
In works with a fantastic bent, this may be a cue for a younger sibling to suddenly come into the picture through supernatural or superscience-y means. In less-fantastic works, it's often up in the air whether the kid gets their sibling or not. Nor is there any guarantee that, should they get their wish, they and their new sibling will get along the way the older one dreamed.
- Chocotto Sister is about a boy who always wanted to be an older brother, but who never got a younger sibling... until one day, in his college years, Santa Claus gives him a little sister for Christmas.
- In Magical Girl Lyrical Nanoha The MOVIE 1st, it is revealed that Alicia Testarossa always wanted a little sister (which is exactly what Fate is to her), as Presea remembers while plummeting to her death.
- In Baccano!, Isaac and Miria receive a letter from Ennis that mentions her sadness over her "brothers created before her, who [she] never got to meet." They assume she's asking them for a baby brother. And so they bring home Czeslaw.
- Part of the reason why Kaguya tries to be a Cool Big Sis for Kei in Kaguya-sama: Love Is War is out of her long standing desire for a little sister (that, and she thinks it would get her closer to Shirogane). This happens to be mutual, but she and Kei seldom have the opportunity to meet.
- In Tsukiuta, Yoru is an only child who wants siblings. This is part of why he dotes on the other Procellarum members as Team Mom.
- In her previous life, Katarina My Next Life as a Villainess: All Routes Lead to Doom! was the youngest of three children and had always asked her parents for a younger brother or sister. As such she is incredibly happy when she meets her adoptive little brother Keith for the first time (with a hint of dread due to him being responsible for her death or exile in several routes). She stands in direct contrast to the original Katarina, who bullied Keith out of hatred for him taking away their father's attention.
- From Kill la Kill AU, Nui wanted another little sister and she got one, making that played straight. However, this is justifiably averted with Satsuki, having to live with Ryuuko and Nui.
- Meet the Family, a My Little Pony Friendship Is Magic fic. Rainbow Dash and Soarin', recently engaged and having adopted Scootaloo, find she left a note on Rainbow Dash's door saying "Little brother please". Rainbow Dash has a talk with her and tells her it probably won't happen for at least a few years, explaining that having a foal would be hard on her body and make it more difficult for her to do her job for a while. Fortunately, Scootaloo understands (despite still not knowing exactly HOW foals are made).
- Played with in TRON: Endgame Scenario: Flynn explains that Tron and Yori look like Jet's parents because they were created by them. Jet is delighted.
"This is the best birthday gift ever! Thank you!" He hugged his godfather.
Kevin laughed. "I know the action figures are cool, tyke."
"Not the action figures - a super-cool brother and sister. I'm not alone. And I'm gonna meet 'em someday. That's the best gift ever!"
- In the film The Hunt for Red October, Jack Ryan tells his CIA boss that his daughter ("a very precocious five") asked him and his wife to "buy her a baby brother" and settled for them buying one for Stanley (her teddy bear) instead. At the close of the film, Ryan is shown sleeping on his flight home with a teddy bear in the next seat.
- At the end of the remake of Miracle on 34th Street, Susan remarks to her mother that her Christmas wishes were a house (instead of their trendy apartment), a dad, and a baby brother. Since her mother marries her longtime boyfriend on Christmas Eve, and Christmas morning finds them moving into Susan's dream home, it's heavily implied that the mother is pregnant.
- Home Alone has a scene where Kevin is watching Johnny Carson read kid's letters to Santa. One reads "Dear Santa, last year I asked for a baby brother and I got one. This year, I just want Play-Doh."
- In The Dresden Files short story It's My Birthday Too, Harry reveals that he wished for a brother when he was a child in the orphanage after his father's death. Ironically (and heartwarmingly), the person he's telling this story to is his long-lost and recently found older brother Thomas.
- One adventure of The Baby-Sitters Club has Mary Anne and Dawn wanting their parents to have a baby so they'll be able to baby-sit him. They come to their senses by the end of the book.
- In The Horse and His Boy, it's implied that one reason Prince Corin is so happy to find his long-lost brother is that there's finally a boy his age around that he can do rowdy shenanigans with. Even before he knew Cor's identity, he marveled at the freedom their ability to Twin Switch allowed him...
- In The Munsters episode "Eddie's Brother", Eddie, suffering from Only Child Syndrome, tells his parents he wants a little brother. Herman and Lily both faint.
- On America's Funniest Home Videos, one clip of a couple telling their 7-year-old son that he soon would have a little brother, the kid exclaimed "Way to go, dad!" and gave his dad a high-five.
- In one episode of Girl Meets World, Auggie asks Cory and Topanga more than once to make a little brother for him.
- The seventh edition of annual Dutch children's choir project Kinderen voor Kinderen included a song called "Ik ben toch zeker Sinterklaas niet" (roughly, "Do I look like Santa Claus?"). The lyrics kick off with little Sascha's wish list: a baby brother, and a pretty red bike, and a giant teddy bear, in that order.
- In Calvin and Hobbes, Calvin once tells his mother he wishes he had a little brother. "You want a new friend to play with?" "No, I just want somebody small I could beat up." The next panel is Calvin's dad at work telling his wife they'll talk about that operation later.
- Subverted later when Calvin's Mom is sick. Hobbes suggests she might be pregnant, and Calvin panics.
- Tomorrow, the World! by James Gow and Arnaud d'Usseau:
Michael: Pat worships you. She comes home from school every day telling me you're the only teacher who has any sense. What's more, she's asked me to get married. To almost anybody! She wants me to have more children. Three of them, to quote precisely.
Michael: As soon as we're married, I'm sure she'll take it up with you.
- In Hamilton Little Philip tells his father in a poem he wrote "I have a little sister but I want a little brother." The real life Philip Hamilton would have 5 younger brothers, one named after him after he died in a duel.
- Many of the "rival children" in Harvest Moon: Animal Parade express a desire for younger siblings, but the two who fit the trope most closely are Lucy and Dakota. Lucy asked her parents, and they agreed, but never have any luck having a second because Status Quo Is God. Dakota, meanwhile, went all the way to the Harvest King to ask for a little sister, but he told her there was nothing he could do unless her parents started getting along first.
- In Fire Emblem Awakening, if Yarne is paired up with his father and steps on an event tile, the latter will ask if the former wants something. Yarne asks for "lots of bunny-eared brothers and sisters". This is completely justified, as Yarne's greatest fear (having come from a Bad Future where his mother died) is the extinction of his kind.
- A running joke in the Neptunia series is Vert wanting a little sister of her own. This usually takes the form of trying to sweet-talk Nepgear into the role. She's also been known to make an offer to other girls who catch her eye.
- In Drowtales, it's considered good luck to have twins or a similar - age sibling. As a result, the Sharen clan has the practice of a "protector twin" (adopting - or buying - a child, usually from a servant family) to give their own children a chance to have a same - age sibling. Unfortunately, this often results in sibling rivalry, ending with the death of the protector twin at the hands of the former child, or (less often) vice versa.
- In Something*Positive, Rory decides he wants a little sister; his mom doesn't seem interested, but when his Parental Substitute Davan gets engaged he immediately starts suggesting he get his fiancée, Vanessa, pregnant. Vanessa, who doesn't want kids, agrees as long as Rory is present at all her births—then shows him a video of what the birthing process looks like.
- Chakona Space: Chakat cubs asking their parents to get busy giving them a little sister.
- One episode of The Adventures of Jimmy Neutron involved the title character asking his parents for a little brother. Since they politely declined, he used his mad science to make a robotic little brother named Brobot. Brobot didn't stick around on Earth, but did become a minor recurring character.
- One episode of Rugrats involved Tommy really wanting a little brother. He then thinks that a bird's egg is his little brother Milton. The egg was just a baby bird, but he did end up gaining a younger brother named Dil after the Revival.
- Angelica's the only main child character in the series to stay an only child throughout it—most of the time, she was thankful for her status as an only child (like the episode where Charlotte thought she and Drew were going to have another baby but later turned out to be a false alarm), but there were some episodes where she expressed a desire for a younger sibling (like the episode where she and the other kids think human babies come from eggs). There was also an episode where Angelica, realizing that she's the only one of the kids to be an only child, is genuinely saddened about not having any siblings—but Tommy helps her to feel better by pointing out that since she occasionally picks on them, but still cares, she's really like a big sister to all of them.
- The Oh Yeah! Cartoons short Zoey's Zoo involves a little girl who keeps tons of animals in her own personal "zoo," because her parents (or at least her mother, whom we only ever see) never caved in to her desire for a little brother. Doesn't stop her from asking about it incessantly, though.
- Littlefoot in at least one of the The Land Before Time sequels has shown interest in wanting a sibling. It doesn't help that he's one of the only main characters in the series (except for Chomper) to be an only child. He DID get a stepbrother when his long-absent father Bron returned in the tenth film, and at Littlefoot's urging, adopted Shorty, a brachiosaurus who had come to view Bron as a father.
- Once on The Simpsons Bart is upset about being the Outnumbered Sibling, and tries tricking his parents into having another baby. Eventually, Marge confronts him about what's going on and, while certainly sympathetic to how her son feels, explains that she and Homer are fine with just three kids. Also, Marge explains that on the chance that she and Homer do ever end up having another baby, their fourth child might end up being a girl instead of a boy (which leads to Bart having a fantasy about having three sisters). Bart winds up going to the orphanage and temporarily adopting a brother instead.
- Zig-Zagged in the Family Guy episode "Emission Impossible": First, it's inverted when Stewie hears his parents decide that they want to have another kid, and tries sabotaging any and all attempts to conceive another child. But after meeting Bertram, one of his possible future siblings inside Peter's testicles (long story), Stewie starts embracing the idea of having a younger sibling. But at the very end of the episode, he changes his mind again.
- Eventually, thanks to a mishap at the sperm bank and a lesbian couple, Bertram is born. Guess how that goes.
- An episode of Arthur sees Sue Ellen expressing a desire for a sibling after she realizes she's the only one out of her friends who's an only child. She tries pretending her friends are siblings, but gives up after an attempt to babysit DW goes horribly wrong. Her parents later cheer her up by signing up to sponsor a Tibetan boy, whom Sue Ellen can view as a little brother.
- This was a trait of the titular turtle of Franklin throughout the first four seasons of the animated series. At times he had a couple of sibling surrogates, first in his best friend Bear's little sister, Beatrice, and also in a guest-star youngster character named Squirrel. The Franklin and the Green Knight movie deals with him at first being excited about finally getting a sibling, then becoming worried when he learns that babies get a lot of attention, even before they're born. Franklin's Magic Christmas sees him dealing with jealousy issues with his new sister, Harriet, who is now toddler/early-prescchooler age thanks to a combination of Comic-Book Time and Soap Opera Rapid Aging Syndrome. The fifth and sixth seasons of the program, as well further specials and the spin-off series Franklin and Friends have him, in general, settled comfortably in the role of caring big brother. The Franklin picture books do hint at this trait, but it's much more prominent in the animated series.