Julia Mesina, her husband, and their three young children faced a dire situation. He'd lost his job, and their savings soon dried up. His parents, in Naperville, Ill., offered to help out. Before long, the young family moved in.
Scott McDowell, on the other hand, says he needed a break. The student at the Berklee College of Music also needed to save money - a difficult feat while paying rent in Boston. He decided to move back home in Marin County in California for a year.
Melody, a senior at the University of Southern California in Los Angeles, never even left home. She stayed with her mom during college to save on room and board, but it strained their relationship; Melody suspects her mother still sees her as a teenager.
For those who remember adulthood as beginning definitively at 18, it's a different world today. Julia, Scott, and Melody are among a growing number of 20-somethings who rely on their parents - emotionally and financially - years after they are legally considered adults.
Between 1970 and 1990 the number of 20-somethings living at home increased by 50 percent, according to the Institute for Social Research at the University of Michigan. Today, 63 percent of college students say they plan to live with their parents after graduating, according to JobTrak.
Young adults are flocking back to the nest for varying reasons, but the trend is now so pronounced that many sociologists and psychologists no longer define them as full-fledged adults but rather as "emerging adults," a term coined by sociologist Jeffrey Arnett.
"I became convinced that it's a mistake to just talk about them as making a transition to adulthood," says Dr. Arnett, at the University of Maryland. "It's really a separate period in life. They're not settled into a long-term occupation. They're not married by and large. Their lives are still very much in flux."
While a lagging job market, unaffordable housing, and modest first incomes are obvious factors, social expectations and parent-child relationships have also contributed to what Arnett calls a "quiet revolution."
The shift has more to do with parenting than with money, says Daphne Stevens, a psychotherapist in Macon, Ga. "Speaking as a baby boomer, I think we just wanted to be buddies with our children," she says. "We didn't want to be old like our parents."
Susan Shaffer, coauthor of the book "Mom, Can I Move Back In With You?" to be released in May, couldn't agree more. "Our generation grew up with very clear expectations - an inevitability of living on our own when we reached our 20s. Our children have grown up with a very close generation, where the parents were highly involved. And that didn't stop at some mythical, magical age."
In many parts of the world, children rely on their parents well into adulthood. In Canada, for instance, 41 percent of 20-somethings live with their parents, according to the Canada Census Bureau reports. In several European and Asian cultures, many children don't leave the house for college at all.
But in America, where previous generations of young people have reached traditional markers of adulthood - a career, a home, a spouse - just out of high school or college, staying close to home isn't always easy - for the parents or their children.
When Mrs. Mesina moved in with her husband's parents, it was one of the most difficult choices she made in her adult life. Not only do she and her husband have less privacy in her parents-in-law's home, but she also feels a twinge of guilt for taking up their space, cutting into their retirement savings, and simply relying on them at all.
"Two families coming together is a hard thing," says Julia, a stay-at-home mom. "We'd like to let them have their space and do what they want. They worked their lives, and we want them to use their money in ways they want."
The time to move out is near, Mesina says, for the sake of her family as well as her parents-in-law. "People have to learn how to live with what they have as much as possible," she reminds herself.
When Mr. McDowell moved back home, it was not out of necessity but rather the most practical way to save money. The California native hadn't yet graduated from Berklee in Boston, but he had to undergo an operation and wanted to do it at home.
"I needed a break," he says, now back in Boston after a year of living with his parents in California's Marin County. "I had gone to school straight through the summer, so I just needed time away from school.... I also had a lot of different projects and ventures that I wanted to explore, and I didn't have time to do that while working hard to pay an expensive monthly rent."
A large factor - some would say problem - is that many parents don't teach their children how to be fiscally independent, say Jon and Eileen Gallo, founders of the Gallo Institute and authors of "Silver Spoon Kids."
"Our book is about growing up in an affluent time, even if your family isn't affluent," Ms. Gallo says. "How do you raise children in this kind of environment?"
Her husband says parents should introduce the concept of money and budgeting to their children at an early age.
"We'd have fewer kids moving back home if they were aware of what the learning curve looks like," he says. Because parents "don't teach the rudiments of dealing with money, i.e., budgeting, cost of credit," children can remain financially dependent until their mid or late 20s.
But Arnett defends the close relationship between 20-somethings and their parents today. "Emerging adults tend to get along better with their parents than adolescents do. It's less hierarchical."
But moving in with parents isn't always the best option, he says. "It still cramps the style of emerging adulthood. You're still going to get comments on how you're spending money, what time you're coming home, why you're eating that doughnut. Most emerging adults would prefer not to have that sage advice imposed at that point."
Melody, who was once prom queen of her high school in Los Angeles, didn't leave home at all. She avoided costly dormitory rent and grocery bills by staying with her mother. But Melody, who asked that her last name not be used, was missing out on the social aspects of college life.
As time passed, her relationship with her mother grew strained. Because she never left home, she worried that her mother saw her as an adolescent. She began to resent her curfew. Eventually, disagreements between Melody and her mother became so fierce that they wouldn't talk for days. She felt she had to leave.
"I'm scared though," she says. "I can't do things that other people my age can do. I haven't learned how to do laundry or cook. I can't even make pancakes for myself."
Parents, of course, face similar hurdles in learning to handle a young adult who is dependent in some ways and independent in others.
Ms. Stevens, a mother of three, one of whom moved back home recently, sympathizes with parents, many of whom struggle to adapt to life with their adult offspring: "I ... tell parents that the story is never written. Children are always doing their work growing, and we're always doing our work growing, and everything we do, and every way we've been hurt, can become a way of learning."
In the grand scheme of things, Stevens supposes, this adjustment is the flip side of the empty nest syndrome. Major life changes are always difficult; kids going, kids coming, the constant need to be flexible. But while leaning on a parent - or even a child - has its advantages, "None of us feels good about ourselves when we are more dependent on other people than we need to be," she says.
• Sheera Frenkel contributed to this report.