It came as no surprise to Pikesville resident Charlene Mazer when her daughter Jenna Kellam, 21, moved in with her in May after graduating from Tulane University without a job lined up. "I expected her to come back home," Mazer said.

But when children return, there are a host of new issues: Should they pay rent? What changes to the house will be necessary? What are the house rules?

Such "boomerang" children are now the norm. A survey by MonsterTrak, a student and alumni job Web site, found that 60 percent of 2005 college graduates planned to move back in with their parents after graduation, as did 61 percent of 2003 graduates and 63 percent of 2001 graduates. And according to the Census Bureau, in 2003, 50 percent of all 18- to 24-year-olds and 27 percent of 18- to 34-year-olds were living with their parents.

Young adults return to the nest primarily for financial reasons, said Nan S. Mead, director of communications for the Colorado-based nonprofit National Endowment for Financial Education. "Usually an adult child moves back home because he or she is experiencing financial hardship of some kind," she said.

For many young adults, however, returning home may not be the result of an economic crisis "as much as a stage of self-exploration," author Jeffrey Jensen Arnett said . "They don't want just a job," he said. "They want something more like a calling, an expression of their identity that they find more fulfilling."

Moreover, the stigma of returning home is less than it was in the 1970s. "There is no longer a sense among 18- to 25-year-olds that they're failing to become adults at the proper age" by moving back in with Mom and Dad, said Arnett, who wrote "Emerging Adulthood: The Winding Road From the Late Teens Through the Twenties" (2004, Oxford University Press).

Whatever the reasons for the return, young adults and parents should realize that life under the same roof will be different from when the children were teenagers. "The kids are used to coming and going on their own and using space as they please, and parents are used to a certain order in their household and to not worrying about them at 1 a.m., " said Karen Levin Coburn, coauthor of "Letting Go: A Parents' Guide to Understanding the College Years," (Fourth Edition, 2003, HarperCollins Publishers).

Parents have to recognize that they cannot 'control' their grown children," said Karen Fingerman, author of "Mothers and Their Adult Daughters: Mixed Emotions, Enduring Bonds" (2002, Prometheus Books). "Having the child move back home makes the grown son or daughter more of a roommate, not a child again."

That's how Charlene Mazer viewed the situation when Jenna moved back in. "We were more like friends in an adult relationship than like parent and child," Mazer said.

One suggestion: Charge rent after a young adult moves back home, either in the form of a monthly cash payment toward the mortgage or as a regular contribution toward food and other expenses, advised Mead of the National Endowment for Financial Education. If your child doesn't have a job, require a routine of chores, such as babysitting, yard work or technology assistance, she said. Either way, set the terms in writing shortly after the young person moves in and have both a parent and child sign the document. The goal is to teach financial responsibility and prevent the young adult from believing that "it's okay to rely on Mom and Dad maybe forever," she said.

Pennsylvania mother Linda Bips collected rent from her daughter Jessica Wallitsch after Jessica, then 23, moved back to Bips's two-bedroom apartment in 1999 after graduating from Muhlenberg College and teaching in Africa for a year. "I wanted her to understand how much she needed to earn to live on her own," Bips said. Jessica paid a monthly amount that totaled 25 percent of her net monthly income from substitute teaching jobs.

"She resented paying rent and thought it was unfair since her friends were living rent-free. But I didn't view it as depriving my child, but rather teaching her some adult responsibility. I'd absolutely do it again," said Bips, author of "Parenting College Freshmen: Consulting for Adulthood" (2002, self-published).

Some hold a different view. "Yes, the relationship has changed, but the world will teach financial responsibility soon enough," Arnett said. Collecting rent might just make it more difficult to get them to move out, he said. Nor is he a big fan of mandatory tasks for young adults. "They are too old for chores and probably won't be there very much anyway."

It's wise to make some design and room changes when grown children return, advised H. Don Bowden, an Alabama-based architect and interior designer and a past national president of the American Society of Interior Designers. Designate certain rooms in the house as common living areas and other rooms as belonging to individual family members. For example, you might tell your son or daughter that everyone can use the kitchen and living room "but while you're home you use the den for entertaining," he said. Also, try to provide the returning child with a separate entrance, perhaps in the basement or over the garage, he suggested.

In the young adult's bedroom, consider a pull-out sofa or even a futon couch instead of a bed, said Sarah Van Arsdale, senior staff writer at New York-based Designer Monthly magazine. Then you can easily turn it into a sitting room, guestroom or home office once the child moves out.

But don't make any design changes too hastily, particularly in a bedroom, cautioned Alexandra Robbins, author of "Conquering Your Quarterlife Crisis: Advice From Twentysomethings Who Have Been There and Survived" (2004, Perigee Books). Young people returning home after college find that their world is scary, confusing and uncertain, so "if their childhood room is still there, they still feel like they have a home base," she said.

At a minimum, parents and young adults should have some agreements on issues such as use of common property, family meals and schedules, several experts said. "They need to talk about how they can live in the same house with the young person having as much freedom as possible and the parent having as much freedom as when the child was away," Coburn said. It also makes sense to set a target move-out date so resentments don't build up.

When parents view the young adult's return as a temporary arrangement that will last for less than a year, which is the typical scenario, they can enjoy having another chance to bond with their offspring. That was the case for Bips, whose daughter stayed with her for six months before moving to her own apartment. Having Jessica back home "provided some of the cement for the close adult relationship we have today," Bips said.

As for Mazer, her daughter Jenna got a full-time job in July and is moving out this month to an apartment in Baltimore. She wants to be on her own and not live in the suburbs, her mother said. But Mazer is already wistful about Jenna's departure. "I didn't want her to leave so fast," she said.