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.
After the four children are kicked out of their home by their parents, the children are desperate to find new parents and think of a plan to 'orphan themselves' by sending their parents to a deadly vacation so that they can die. They see a travel agency after wandering homeless in the streets of a busy city, and Tim says, 'We can send them away. What if we orphaned ourselves?" They then sneak back into their home (still kicked out) without their parents' knowledge, and Tim states, "We shall craft a murderous adventure." He then states, "A romantic getaway, hiding deadly orphaning opportunities. If they do melt in the hottest place on earth ( a scene is shown of the parents melting in lava)...they shall drown in the wettest (two sharks are shown eating the parents who are in a boat)...Cannibals will feast unless they freeze in glacial ice (a scene is shown where parents are being boiled in a large pot while cannibals dance around the fire with a knife in hand, then it shows them freezing in a glacier)...or dissolve in fields of acid (parents are shown as their skin dissolves due to the acid)...they shall not escape the bears (two large bears being aggressive)...we have saved the deadliest spot for last, the alp." Then Jane points to a picture of the alps and says, "He who goes up does not come down." After this point, the kids are on a race to get orphaned so they no longer have to deal with their unloving and selfish parents.
A cat narrates the story of the Willoughby siblings: Tim, Jane and twins both named Barnaby. The Willoughby family legacy has an accomplished history, but the children's parents only care about each other. They despise all children and deprive the siblings of love, food and music. Tim longs for his family's past glory.
Jane discovers a baby on the family's doorstep. She brings the baby inside despite Tim's warnings, and the baby wreaks havoc. The Willoughby parents throw their children out of the house, forbidding them to return unless they get rid of the baby. The children follow a rainbow to the doorstep of Commander Melanoff's candy factory, and believing it to be a suitable home, name the baby "Ruth" and leave her there. On their way home, the siblings hatch a plan to improve their lives by getting rid of their parents. The siblings put together a vacation brochure full of deadly destinations that could potentially kill their parents and make them orphans.
Their parents are excited by the brochure and leave immediately. Tim tries to take care of his siblings alone, but flounders until the nanny hired by their parents arrives. The nanny, Linda, proves to be much warmer and more caring than their parents, and Jane and the Barnabys warm up to her almost immediately; Tim, however, remains distrustful. When Linda learns about Ruth, she rushes to the candy factory with the children in tow. Melanoff explains that he originally intended to hand the baby over to the Department of Orphan Services, but grew attached to her; Linda is assured that Ruth will be well cared for in the factory.
Meanwhile, the Willoughby parents have somehow survived several hazardous destinations, but soon discover they're out of money. Unwilling to return home, they decide to sell their house in order to further finance their vacation. They tell Linda by voice message, and Linda assures them she will take care of the children. Tim gets Linda's cell phone and finds the voice messages. He mistakenly assumes Linda means to dispose of the children, and secretly calls Orphan Services to report her.
The Willoughby parents hire a Realtor to sell the house to potential buyers, but the children scare off all but one family. Linda scares the last family off for them. Tim finally realizes how much Linda cares. However, Orphan Services arrive in response to Tim's call. Heartbroken by Tim's betrayal, Linda leaves in tears, and the Willoughby siblings are forcibly taken away and placed in separate foster homes until their parents return. Tim repeatedly runs away from his well-meaning foster families and runs to the Willoughby home just in time to watch its demolition. Orphan Services decides to detain him in a cell at their Headquarters.
The narrator cat finally intervenes by giving Tim's helmet to Linda. She decides to reunite the children. Disguised as a janitor, Linda sneaks into Tim's cell, reconciles with him, and breaks him out with the helpers in pursuit. Linda then retrieves and reunites the other Willoughby children.
The children decide to go back to their parents so that Orphan Services will leave them alone. With the help of Linda, Ruth, and Melanoff, the Willoughbys build a dirigible to rescue them from the "Unclimbable Alps" in Switzerland (shown and pronounced as Sveetzerlünd), which is the final and deadliest destination on their parents' trip. The siblings decide to take the dirigible and leave the adults and Ruth behind. As they reach their destination, 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 and the cat save them. The children confess that they sent them away but hope to reunite as a family. However, their parents are selfish as always, stealing the dirigible and abandoning the children. However, not knowing how to steer the dirigible, Mr. and Mrs. Willoughby crash into the ocean.
With no way off the mountain, the siblings start to freeze to death, with no way down back, Jane sings for them. Thankfully, Ruth, Melanoff, and Linda followed the dirigible and heard Jane's song, finding the siblings just in time. Now officially orphans, the Willoughbys are adopted by Linda and Melanoff, living much happier lives together with Ruth and the Cat at Melanoff's candy factory. Meanwhile, Mr. and Mrs. Willoughby are shown to have survived the dirigible crash and are stranded at sea, whereupon they are eaten by a shark.
