The chapters can be summarised as such:
- What's That Noise?!: Mr and Mrs Cake start potty training the twins. When they hear and see the toilet flushing, they think it's a dangerous monster and tell Pinkie Pie, who convinces them it isn't.
- Pound's Pain: Pound, not wanting to use his potty, decides to hide diapers and put them on when he needs to do his business. While playing, he has to poop, which feels painful to him, and he starts putting his plan to use, but after he uses the diaper, he sits on Pumpkin's potty as a joke and cannot get up. when Mr Cake discovers him, he gives up.
- Pumpkin And The Potty: The next day, Pumpkin, who, unlike her brother, wants to use her potty, is playing with Pinkie Pie when she too needs to poop and accidentally uses the potty with her diaper still on.
- Down The Hooooole!: While home alone with Pinkie (who's checking on cupcakes), the twins have fun flushing items (and Gummy) down the toilet, but when Pound Cake flushes his sister's favourite rubber chicken down the toilet, she gets angry and flushes him down the toilet, calling him a turd. However, she then feels guilty and using her own logic (thinking she feels like a turd, turds need to be flushed, therefore she needs to be flushed), flushes herself down. Luckily, Pinkie Pie fishes them, Gummy and the items and toys out of the sewers.
- The Streak: After getting out of the sewer, the twins get told off by Pinkie Pie, and get made to use their potties with the promise of cupcakes. Pound doesn't believe he will be getting cupcakes, but Pumpkin persuades him to use his potty by rewarding him with the chance for both of them to run around without diapers after their bath.
- To Snatch A Potty: That evening, Pound steals Pumpkin's potty and they find out the next morning and Pinkie reckons it was stolen by a creature called a "potty snatcher". When he tries to steal his own, he gets caught by Gummy and Pinkie.
- You Can't Take Your Potty With You!: Pound Cake gets told off and made to return his sister's potty. She's mad at him, but he still thinks the potty is stupid, so in order to make him use his potty, she magics it so it gets stuck to his butt, lying that it will make it flush. His parents cannot unstick him, so he has to wait for Twilight to come.
- Everypony Poops: After being unstuck, Pound is mad at Pumpkin, who apologises after he threatens to flush her down the toilet. The next morning, Mrs Cake has to poop and goes off to do her business, but due to acting strangely before going off (quite different from how they act when they need to go), the twins worry about her. They find their mother on the toilet.
- To Flush Or Not To Flush: After Pound Cake says he plans to become a rebel and steal everyone's potties, flushing everyone who disagrees, Pumpkin steals his pacifier, decides to do something bad to it, and debates over whether or not to flush it, eventually deciding to. He gets it back, but not before contemplating running away.
- Starlight the Foalsitter: On the one-month anniversary of the twins' potty training, their parents go off to a bakers' conference and, with Pinkie Pie unavailable, they leave them with Starlight Glimmer. Starlight puts the twins on their potties and reads a book titled "Everypony Poops", which bores them. They trick her by pretending they flushed themselves, but things turn serious when Starlight apparently faints. Thankfully, she gets up promptly.
- Missed!: Starlight continues to foalsit the twins, and while playing, Pound Cake has to do his business, so he tries using his diaper again. He poops his diaper, but wets the floor.
- Pound's New Diaper: When the twins' parents get back, they hear about Pound pooping his diaper and wetting the floor and decide to take his diapers away. He makes a diaper out of stuffed animals and poops in it, but it doesn't work, and they clean it up.
- You Only Flush Once: Pumpkin rides Gummy into the bathroom and tries to use the toilet, but falls in, which makes her sad because she thinks she has to be flushed. However, Pinkie Pie saves her.
- That's Not A Potty! Part One (The Flowerpot): Pumpkin Cake is sad that her brother won't use his potty, so she gets put outside to play with her brother (and she gets to go diaperless) to cheer her up. However, she finds herself needing to poop and goes in a flowerpot, believing herself to be "fertilizing the soil". Pound gets her some wipes by purposefully getting sand in his diaper.
- That's Not A Potty! Part Two (The Teapot): After Pumpkin wipes herself, their parents go out for their anniversary while Pinkie Pie takes them to the mall to buy a toy each. Soon, Pound Cake needs to pee but doesn't want to tell Pinkie because he still doesn't want to use his potty, so he goes in a teapot.
- That's Not A Potty! Part Three (Caught): Pound buys a teddy bear and Pumpkin, unfortunately, buys the teapot Pound peed in, so he gets caught.
- Fluttershy And The Case Of The Missing Potty: While the Cakes and Pinkie Pie try to work on getting Pound Cake to use his potty, Pumpkin Cake gets sent to stay with Fluttershy, whose animals wonder what Pumpkin's potty is for. Eventually, Discord finds it.
- Pony Goldberg Would Be Proud: While Pumpkin is staying at Fluttershy's, Pound still refuses to use his potty. Mrs Cake starts to use reverse psychology on him, and it doesn't work at first, but then he feels guilty when she says, "I only gave birth to you, fed and nursed you, bathed you, played with you and changed you.", so he uses his potty. Then, he sees an illustration of a machine made by someone named Pony Goldberg and decides to make a machine to make the potty land on his sister's head, with Discord's help.
- Check-Up And A Visit To Twilight's: While Pound Cake gets his checkup, and Mr Cake and Pinkie Pie are shopping for flour, Pumpkin is left at Twilight's house. Twilight lets Pumpkin keep Smarty Pants.
- Pumpkin Makes A Decision: When the twins get home, they have a little argument but make up. When they make up, Pound suggests Pumpkin use her diaper at night, and she mulls it over but eventually does.
- When In Public: Mr Cake takes his daughter to the store to buy pull-ups, and she uses the toilet.
- Two Foals, One Outhouse: Twilight foalsits the twins after their trip to the store, but she's turned into a kangaroo. She takes them to the park, where they have to share an outhouse.
- Toilet Trouble! Part One: Flushing Pumpkin: Twilight takes the twins home. They wake up in the night to use the bathroom and Pound tries to use the toilet but nearly falls in. Pumpkin tries to save him, but falls into the toilet. When he tries taking her out with the rubber chicken, he accidentally flushes her.
- Toilet Trouble! Part Two: Pound Takes The Plunge: Pound saves his sister with a plunger.
- Potty Training Pinkie Pie Style: When Pinkie Pie pretends to be a professor, teaching the twins to use their potties, they pretend they have no idea what she's talking about, so she puts on a diaper to show them what to do, and they treat her like she's their age, leading to her wetting herself.
- When Tickle Monster Attacks: Partly as punishment for the babying, but also partly as just a friendly joke, Pinkie Pie pretends to be a "tickle monster" and tickles the twins.
- Scootaloo The Potty Mouth: While the Cutie Mark Crusaders visit, they talk about the wacky and annoying things their families do, and Scootaloo says that it is lucky Rarity is not her big sister or she will "end up peeved with her in a week", which shocks everyone else because 'peeved' is a cuss word in Equestria. The twins overhear the Crusaders' conversation and wonder what 'peeved' means and what a 'potty mouth' is. Mrs Cake is shocked when they ask her what it means and tells her to foalsit them when she and her husband go out to dinner. Scootaloo tells the twins what a potty mouth is.
- The Exploding Diaper: The next day, Scootaloo tells the Cake parents the story of how, while being foalsat, the twins inflated Pound's diaper with helium, leading to it exploding.
- Flurry Heart's Royal Flush: Because Sunburst has the flu, Shining Armor and Princess Cadence leave Flurry Heart with the Cakes. After a conversation, they flush her down the toilet, but she teleports herself out.
- Oh Deer! Part 1: After the royals leave, Starlight enters but she seems out of sorts (her horn is leaking sparks, she's sneezing and coughing, and she has bags under her eyes). It turns out that she has eye bags because she hasn't been getting enough sleep due to staying up late researching how to turn Twilight back to normal and the rest of the symptoms are because she's got something called horn flu, that makes her magic unstable. She sneezes, turning the twins into baby deer.
- Oh Deer! Part 2: Spike, who Pumpkin Cake develops a crush on, tries to help Starlight change the twins back, but fails. Luckily, Twilight succeeds. Starlight gets sent on a trip to be healed, and, due to negative experiences with the horn flu fiasco, decides she has to wait before giving friendship another chance, upon which she'll come back.
- Clothes Make The Pony: The next day, the twins are taken to Rarity's boutique, where she makes them a onesie each. Pumpkin is jealous of Rarity because Spike likes her but she (Pumpkin) likes Spike. While Rarity makes the onesies, Sweetie Belle watches them and they play tag.
- Diamond The Dazzling Foal: Diamond Tiara wants to earn money, so she is asked to foalsit the twins while Mrs Cake gets a checkup. When she tickles Pumpkin, she accidentally turns into a toddler after being zapped by Pumpkin's unreliable baby magic.
- Diamond's Dazzling Diaper Day: Diamond gets diapered, and she and the twins play. When the Cakes go home, they are shocked, but are fine with, Diamond Tiara's regression.
- Diaper Shortage?: Mr Cake discovers that a lot of the diapers are missing. Diamond Tiara is asked to catch the diaper theif, who turns out to be Apple Bloom, trying to dress as a baby to remember her parents.
- Silly Sweetie Belle: While foalsitting the twins, Sweetie Belle ends up with a (clean) Pull-up on her head, she's embarrassed but they keep it a secret.
- In The Eye Of The Beholder: Pinkie Pie comes back from a boat trip she had to apparently cure her of something Starlight did to her while she had the horn flu. The twins then get bored in their playpen and Pound suggests they play-fight each other with plushies. During the fight, Pound gets hit in the eye so his family take them to the doctor.
- Panicking Pumpkin: Pumpkin worries about Pound's eye injury, but he's fine and Pinkie gives her a pep talk.
- A Sick Toilet?: When the toilet doesn't flush properly, Pinkie speculates that it isn't working, and Pumpkin Cake thinks that means it's "sick". Pound Cake thinks she's joking, but is convinced when he overhears his parents talking about it. He decides they need to "save" it and they give it medicine. Mr Cake teaches them that toilets don't get sick.
- The Wrong Potty!: The twins fall asleep that night worried about the toilet, and Pound Cake wakes up in the night needing to do his business and he decides he wants to use his potty but uses his sister's by accident.
- Potty Fever: The next day, the twins get taken to Sweet Apple Acres, while Pound gets put in pull-ups, but has an irritated throat and nose, as well as his forehead being warm. It turns out he has feather flu. He takes a nap, while Applejack runs to get medicine. When Pound wakes up, he hears Granny Smith calling his sister's pee "gold" and worries that he's somehow gotten her sick so that her pee's gone solid. He wants to stop Granny Smith from flushing the pee because he thinks that he needs it to prove to Applejack that Pumpkin is sick, but Granny explains that 'gold' is just an expression her family have for pee.
- A Trip To Cloudsdale: Rainbow Dash suggests that taking Pound to Cloudsdale would cure his feather flu. When they get there, he takes medicine and has another nap.
- The Great Cloud Flush: Rainbow Dash falls asleep due to boredom and Pound wakes up, being slightly, but not fully, recovered. He cannot find his potty, so he goes out and pees on the clouds. He tries to flush them, but blocks the toilet.
- Doggy Style: Pumpkin plays fetch with Winona and then pretends to be a dog. She gets disgusted by seeing Winona drink from the toilet.
- Beware The Butt Ghost!: After Rainbow Dash unclogs the toilet, cleans the clouds and puts Pound Cake in timeout, the twins get picked up by Pinkie and that night, while Pound is using the potty, a mysterious voice claims to be the "butt ghost" who lives in the toilet and tries to get inside ponies' butts.
- Pound, Pumpkin and Ponypalooza: Pinkie Pie takes the twins on a train trip to her family's rock farm. Igneous and Marble play with the twins, and then Pound flies away, so Limestone chases him with a butterfly net and Pinkie tells him off. (Pound's better now)
- Ripped Pants: Everyone eats "rock soup", which appears to act as a diuretic for Pumpkin. Bored, Pound plays for a bit with Smarty Pants. He accidentally breaks her, which makes Pumpkin angry. Limestone fixes Smarty Pants.
- The 'Joy' Of Flushing: Pound Cake is bored, when a colt named Button enters and plays with a device called a joyboy. When he calls the twins stupid, they take the joyboy and flush it, so Mrs Cake spanks them.
- Foalhood's End: Button receives a new joyboy and apologises for calling the twins stupid. When Button's mother says that her son is growing, Pound realises he is too and he and his sister worry about getting older, so they use diapers.
- A Look Back: Five years later, the twins pretend to be toddlers.
