Convinced they’d be better off raising themselves, the Willoughby children hatch a sneaky plan to send their selfish parents on vacation. The siblings then embark on their own high-flying adventure to find the true meaning of family.
The Willoughby siblings – Tim, Jane, and the Barnabys – have terribly neglectful parents who only pay attention to each other. The kids then devise a plan to send their parents on a traveling vacation where they may end up walking to their deaths so that the kids can be orphans. Mother and Father leave them in the care of a nanny named Linda, who proves to be a far better guardian than the two of them. Although Jane and the Barnabys quickly like Linda, Tim is hesitant because he wanted to be in charge.
Mother and Father sell their house to make more money to keep traveling. Linda offers to take care of the children, but Tim thinks it means that she is conspiring with the parents to get rid of them. He calls the Department of Orphan Services, who end up splitting him and his siblings up to separate families. Linda is inspired to help them out, and Tim apologizes to her for what he did and for not trusting her before they go get the rest of the kids. They decide that they have to get their parents back to prove they aren’t orphans when the agents won’t stop chasing them.
The kids team up with candy maker Commander Melanoff to make a dirigible to fly to Switzerland to stop their parents from climbing up a freezing mountain. When they find Mother and Father and try to explain the situation, the two remain terrible as ever and abandon the kids on the mountain and take the dirigible. They end up crashing after realizing they can’t fly it. The kids almost freeze to death until they are found by Linda, Melanoff, and a baby named Ruth that the kids brought to Melanoff.
Linda and Melanoff adopt all five kids so they can have the family they always wanted. Mother and Father survive the crash but are eaten by a shark.
A stray cat narrates the story of the Willoughbys, once an adventurous and loving family for generations. The present-day Mr. and Mrs. Willoughby are too enamored with each other to care for their four children: eldest son Tim, who tries to keep his siblings out of trouble; middle daughter Jane, whose beautiful singing is silenced by her parents; and the inventive but “creepy” twin boys, both named Barnaby. The parents mistreat and neglect the children, refusing to give them food and punishing them by making sleep in the coal bin. After Jane and the twins find a baby abandoned outside, their parents kicked them from the house until they return without the child. They leave the baby, whom Tim names “Ruth”, on the doorstep of a candy factory and the owner, Commander Melanoff, takes her in.
To rid themselves of their neglectful parents, the siblings send them on a “dangerous vacation” by fabricating a travel brochure of volcanoes, bears, and other hazards. As the children celebrate their freedom, a nanny hired by their parents arrives and wins over everyone but Tim. Learning about Ruth, Nanny takes the children to Melanoff’s factory. After saving Ruth from the assembly line, Nanny realizes the child is safe with the loving Melanoff. Mr. and Mrs. Willoughby, having survived the various danger, not wanting to go back to their children but short on funds to continue their trip, sell their house online. Walter informs Nanny in a voicemail, which Tim overhears. Believing Nanny is in league with his parents, Tim reports her as a “bad nanny” to the sinister Orphan Services.
When their parents’ realtor arranges an open house, the siblings scare off potential buyers with a series of traps. Nanny frightens away one last family, convincing Tim that she means well, but Orphan Services arrives. The head agent recognizes Nanny as Linda, an orphan who never found a family who wanted her. Learning that Tim called Orphan Services, Linda leaves and Jane angrily chastises Tim before the siblings are separated and taken to foster homes. Tim keeps running away from his foster families, discovering in the process that the Willoughby mansion has been sold and demolished, and is eventually confined at the Orphan Services center. The cat finds Linda and brings her Tim’s signature helmet, convincing her to reunite the children.
Linda breaks Tim out of Orphan Services and collects the siblings, and Tim apologizes to Jane. He suggests that they find their parents in order for Orphan Services to leave them alone. Linda and the siblings enlist Melanoff’s help to construct a candy-fueled dirigible to travel to “Sveetzerlünd” (a parody of Switzerland), where their parents are scaling the “unclimbable Alps”. Taking flight without Linda, Melanoff, and Ruth, the siblings reach Sveetzerlünd. They follow a trail of their mother’s yarn to the top of the mountain, where they find their parents nearly frozen to death. The siblings save them, confessing that they sent them away but hoping to reunite as a family. Unchanged, Mr. and Mrs. Willoughby abandon their children and take the dirigible, but cause it to fly out of control and crash. The siblings prepare to succumb to the cold as Jane sings, but they are rescued by Ruth, Linda, and Melanoff.
Linda and Melanoff adopt Ruth and the Willoughby children, all living at the candy factory as a loving family. Meanwhile, Mr. and Mrs. Willoughby survived the dirigible crash, floating at sea, and are presumably devoured by a shark. In a post-credits scene, the cat cleans himself until noticing the audience.
The film starts with a stray cat (Ricky Gervais) narrating. He brings us to a home owned by the Willoughby family. Although their family has seen generations of great individuals, the present line has since sullied their good name. Mother (Jane Krakowski) and Father Willoughby (Martin Short) are madly in love but are horribly neglectful parents to Tim (Will Forte), Jane (Alessia Cara), and twin brothers both named Barnaby (Sean Cullen).
Tim is forced to spend time in the coal bin while Jane sings and has a “what if” approach to life. The Barnabys are seen as creepy by their parents. They don’t even bother to feed their kids, which forces Jane and the Barnabys to sneak into the dining room and grab dinner while Tim talks to Mother and Father. They scold the kids and punish Tim, making it seem like the kids are the ones who are selfish. Tim only wants to bring back dignity to the Willoughby name.
Later that night during a heavy rainstorm, the Cat comes across a box left outside the gate that is violently thrashing. Jane and the Barnabys see it and go downstairs to inspect it. She goes out and opens the box, with something appearing to attack her. In the morning, Tim finds his siblings bringing in what was in the box – an orphaned blue hair baby. Tim tries to get rid of it since he knows their parents will punish them for it, but Jane wants to hide her. The Barnabys accidentally let the baby loose, and the parents spot her. The baby then eats or destroys Mother’s beloved yarn, leading the parents to kick their kids out until they get rid of the baby.
Jane follows a rainbow, thinking it will lead them to a good home for the baby. She travels with her brothers and comes across the Melanoff candy factory. They leave the baby on the porch and name her Ruth, because Tim feels that they are ruthless for abandoning the baby the same way their parents have neglected them. Jane rings the bell and leaves with her brothers as the factory’s owner, Commander Melanoff (Terry Crews), opens the door and gets jumped by Ruth.
As the siblings walk home, Jane comes up with the plan to make themselves orphans since she thinks they have it better than they do with the parents they have. She wants to get their parents to go on a vacation to dangerous places so that they can end up “accidentally” leading to their demise. This includes sending them to a volcano, acid springs, a forest with bears, and a freezing mountain in Switzerland (or Sveetzerlund). The kids make a fake brochure and drop it down for their parents to see. They take the bait and call for a cheap nanny to come watch the kids.
After the parents leave, the kids start having fun around the house before being visited by the hired Nanny (Maya Rudolph). Jane and the Barnabys take to her quickly since she admires the twins’ inventiveness and also likes to sing with Jane. However, Tim is less accepting since he wanted to be in charge of his siblings. Nanny feeds the kids oats, but Tim misbehaves and is about to be sent to a time-out before Nanny learns that they have been put in the coal bin. It also leads to her finding out that the kids took Ruth to Melanoff’s, which upsets Nanny.
Nanny takes the kids to Melanoff’s to check on Ruth. Although Nanny tries to take Ruth, Commander Melanoff has quickly come to love Ruth and wants to keep her. Ruth then goes loose around the factory and eats a bunch of candy, causing her to puke a rainbow. Nanny decides to let Ruth stay there, but tells Melanoff to make the factory safer for Ruth and to not let her eat only candy.
Mother and Father enjoy their vacation, even though their tour guides end up suffering gruesome fates thanks to them getting in the way and forcing them into the path of danger. As they are riding across a river, they find that they must cut their trip short since they are broke. Their guide tells them they can sell their old-fashioned house for a lot of money. Mother and Father call Nanny to inform them of their plans. The tour guide also ends up devoured by piranhas.
A realtor comes to sell the house, while Tim finds Nanny’s phone and reads a message saying she will “take care” of the kids, which he interprets as telling Nanny to get rid of them, and that she is just as bad as their parents. He calls the Department of Orphan Services to take them away from Nanny. Meanwhile, Jane and the Barnabys set up traps to scare off potential buyers. They almost meet their match when a perfect, cheerful family comes in and just has fun with their traps. They are then scared away when they go into the attic and hear a spooky voice telling them to leave. It’s Nanny, having set it up to have fun with the kids. Tim tries to call her out and make it seem like she’s trying to get rid of them, but Nanny insists that she wants to actually care for the kids. Unfortunately, a team of agents from Orphan Services show up. They recognize Nanny as a former orphan named Linda, and they play Tim’s message calling them, where he lies about him and his siblings being orphans and that their nanny is bad. The agents make Nanny leave and they take the kids to separate families, but not before Jane blames Tim for all this.
The Barnabys are sent to a family who keep them occupied with TV and the internet, while Jane is left with music-loving hippies, but she is still depressed from everything. Tim has made continuous escapes from foster families and is now left in a cell at Orphan Services. He tries to run back home but finds it getting demolished. Linda starts to leave on a bus out of town until the Cat slides down on Tim’s plated hat down the roof. It inspires her to go back and get the kids.
Linda disguises herself as a guard to break Tim out of Orphan Services. The agents catch them and chat after them, but Linda manages to get them away. They retrieve the Barnabys, but Jane refuses to leave until Tim apologizes for what he did and resolves to get the family together. The hippies cover for Linda and the kids as the agents show up. Knowing that they won’t stop looking for them until they see that they are not orphans. They go to Melanoff’s and construct a dirigible to help fly them to Sveetzerlund to stop their parents from climbing up the mountain.
Mother and Father end up on the mountain anyway and find themselves run out of yarn to lead them back down. They huddle together as they prepare to freeze. The kids take the dirigible when Linda and Melanoff aren’t looking, and they end up close to the mountain but can’t reach a high enough altitude. The Barnabys boost their rainbow and send them to the top. They come across their parents, covered in ice but not having frozen to death because they are still kissing and it has kept them warm. The kids thaw their parents and explain their situation and invite them to come home. Mother and Father look as though they have realized their mistakes and appear to start being better parents, but they throw that opportunity out the window as they push the kids aside and take the dirigible themselves. They get their just desserts when they lose control of it and burst it on the tip of the mountain, sending the dirigible flying away down to the clouds.
The kids try to make it down the mountain, but they are losing their way and have run out of things to keep them warm. As they resign themselves to their fate, Jane sings a personal song as her brothers huddle around and hug each other. Not long after, they are found by Linda, Melanoff, and Ruth, who followed the rainbow trail to find them. They ride Melanoff down the mountain. After realizing they are now actually orphans, Linda and Melanoff agree to adopt all of them, as well as Cat. They soon become a loving family, just as the kids always wanted.
Cat then shows us that Mother and Father somehow survived the dirigible crash and ended up stranded in the middle of the ocean, but still admiring one another. And then a shark jumps out and eats them.
Cat is then seen after the credits licking himself and defending it as he notices the audience watching him.