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In the ad, a slack-jawed 20-something with a three-day growth of beard growls to his parents about the lack of services in their (and his) home, while a cackling grandmother watches from the sidelines. "Whaddaya think this is?" the mother finally asks. "A Holiday Inn?"

While its tone may be exaggerated, the ad does reflect another reality: With the country in tough economic times, more young American adults, over age 18, are returning to the family nest. Some "boomerang" kids may rotate in and out for years, if not decades, changing, for better or worse, the household's dynamics.

And psychologists and other experts say they think terrorist threats may propel more kids toward home.

Many of her young clients, says Mary E. Hotvedt, a Tucson, Ariz., family therapist who is president-elect of the American Association for Marriage and Family Therapy, "have expressed the desire to stay closer to home, closer to family. The reaction is not one necessarily born of fear" but of the need to be with "those emotionally closest to them."

But it's financial pressures that are most likely to send grown children back to the nest. Michael, 28, for example, moved from Michigan to his parents' home north of Phoenix last summer after he lost his job and his marriage failed. He intends to stay just until he can get back on his feet.

Anna, 25, a college student with a part-time job, moved in with her parents in Kensington, Md., last June. "She was having trouble making ends meet," says her mother Patricia. "It's hard to pay for health insurance, student loans and rent on part-time pay."

Historically, the number of boomerang kids rises when the economy turns sour. Under 8 percent of adult children ages 25 to 34 lived with parents in 1970, but the rate began to climb with the lagging economy in the early 1980s, then flattened out in the high-flying dot-com days of the 1990s.

By 2000, when the economy again started to decline, nearly 4 million, or 10.5 percent of the 25 to 34 age group (and 12 percent of those ages 25 to 29) were living in the family home.

"[Today's] students have taken on debt with student loans and credit card bills," says Ken Ramberg, senior vice president of Monstertrak.com, an online consulting and job placement firm. Jobs are hard to get now and harder to keep, he adds, and "young people have seen no loyalty from employers."

Those prospects are driving many students home. A November survey by Monstertrak.com found that 60 percent of current college students plan to move back home after graduation—more than 20 percent plan to stay for at least a year.

Getting married later or working to pay for college can also keep kids at home. So can protective baby boomer parents. They "want to guide their children," says Barbara Coulon of Youth Intelligence, a market research firm. "They want their children to pursue their passion, not simply track down the highest-paying job."

HAPPY, OR UNHAPPY, RETURNS?

The circumstances under which young people return to the family home range from blissful to desperate. A good outcome for everyone, experts say, depends on a family dynamic that was relatively healthy in the first place, and on clear communication and planning.

Occasionally the dynamic is disastrous, like the Cleveland couple who can't get their grown child to budge now that he's parked in the family home.

"I finally suggested they sell their house and move," says Donald K. Freedheim, a Cleveland clinical psychologist who advised the family. "Of course they couldn't do it."

Freedheim has also seen desperate parents threaten to throw their kids' stuff out on the lawn.

Most boomerang families aren't so dysfunctional, and many live in a peaceful, if temporary, state of balance.

Ingrid Lund, 22, returned to her family's home in Washington to regroup after graduating from the University of Michigan in May 2000 because the job she was promised on campus fell through. She works full time and is saving half her paychecks for graduate school.

While the family never formally sat down to decide a time limit, says her father Michael Lund, "it has been understood clearly for some time that this would only go for two years."

Ingrid and her parents bicker occasionally about walking the dogs or making dinner, but mostly they live in harmony. In the anxious days after the terrorist attacks, when her husband was overseas on business, Ingrid's mother Judith Bailey, a lawyer for the Federal Trade Commission, found Ingrid's presence "a quiet comfort."

Ingrid, who's ready to move out now, gives her parents good marks for withholding unsolicited advice—still, they sometimes remind her not to stay out too late.

"They're still parents," she says.

It's been harder for Lorraine, whose 34-year-old son moved to her home in Acushnet, Mass., with his daughters, 4 and 6, after his marriage broke up. Lorraine, 60, wants to be sure her granddaughters have a secure home but has not worked out with her son how long the three will stay.

Lorraine, who had been happily adjusted to her freedom, baby-sits while her son, who works the night shift, sleeps. She does much of the laundry, most of the cooking and most of the disciplining.

"I think my son knows he can't be here forever," Lorraine says. "But I leave it to God."

RULES AND LIMITS

If boomerang kids and their parents want to live in peace, they need to plan, experts say. Living with an adult child "can be an invigorating experience for everybody," says psychologist Freedheim, "but it's important to have a plan and a time limit." (See House Rules.)

Without those, Freedheim says, the regression—a temporary return to a state closer to childhood—that's a normal part of life transitions or stress "becomes a lifestyle."

Even the most unconventional proposal can work if everybody understands the parameters.

When Trixie Kelleter's son announced that he and his wife, who lived in Chicago, were going to have a baby, she was thrilled. When they announced they wanted to spend the summer at her Maine home and to deliver the baby there with only a midwife and family nearby, she was stunned.

Trixie and her husband Bob agreed, with the understanding the kids would return to Chicago after the birth. As the birth date neared, Kelleter was "scared to death." As the labor crept into its second day, a nervous Trixie mowed every inch of the lawn with her push mower, wondering "is this ever going to be over?"

Eventually the baby was born, and the children did return later to their own home, according to plan. While the stressfulness of the birth still lingers, Kelleter says she also relishes the experience.

Her mixed feelings are not surprising. Multigeneration households can be difficult, depriving everyone of their privacy and control over their own lives. But they can also be a place where the generations bestow unexpected pleasures upon one another.

Washington resident Janet Dinsmore credits her daughter and son-in-law with encouraging her to do things she didn't bother with when she lived alone. "I do more," she says. "I walk more, go to more galleries. We all eat together."

The couple moved back to Washington from Boston and moved in with Dinsmore while they looked for jobs. The children got jobs, and soon the three adults will be joined by a baby, due in January.

At first Dinsmore expected the young family to move to their own home. Now, she says, "it's worked out so well it feels natural to be living together."

She says the kids "pull their weight." Her son-in-law recently surprised her by reorganizing a tool bench that hadn't seen order "since 1972," Dinsmore says.

Better yet, he cooks.