A word to Bay Area parents: You may want to hold off on converting those empty bedrooms into offices and exercise spaces.

High unemployment and changing social norms are guiding young -- and not-so-young -- adults to move back home, new census data shows.

"It's almost becoming a normal step," said Joshua Coleman, a Bay Area psychologist who is a co-chairman of the Council on Contemporary Families. "Children leave home and go away to college -- or don't -- and then move back in with the parents for a while."

Almost 31 percent of all children living at home in California are 18 or older -- up 7 percent from 2000 and reflecting a national trend. Over the past decade, the number of adult children living with their parents grew by 21 percent in the East Bay and 14 percent in Silicon Valley.

This is puzzling to parents who, in their time, couldn't possibly envision moving back in with mom and dad.

"We all worked," said Linda Hodges, 49. "The minute we could, we got apartments to live the single life."

Two of Hodges' five adopted and biological children have moved back to her San Leandro house; a third recently lost his job and may return home as well.

"The job market is just so tight," Hodges said. Many of her sons' friends also live with their parents, she said.

Economic reasons

Nearly every Bay Area city saw a rise in "boomerang kids" over the past decade. Adults now account for more than a third of children living at home in San Leandro, Hayward, Union City, Hercules, San Bruno and San Francisco, among other cities.

The U.S. Census Bureau attributed the trend mostly to economic factors in a report this spring, noting that adults who are poorer or less educated have the greatest odds of living in what is called a "doubled-up household."

Liz Lynn and her husband live with her parents in San Jose. The 34-year-old made the move two years ago to save for a down payment for a house.

"It allows us to gain some footing and be able to get into a place in a decent neighborhood. We were all of the mindset that renting is just throwing money away and not helping us. We decided if that's what it takes, then that's what it takes," she said.

Not everyone who moves home is desperate. About half of grown children who live in their childhood home have full- or part-time jobs, according to a 2009 Pew Research Center survey.

Josh Rose, director of the Richmond- and Antioch-based Family Works Community Counseling, says he sees adults moving home for psychological support or to transition between jobs or relationships. Some even move back to support their parents or protect them from threats such as domestic abuse.

"The decision is rarely only a financial choice," he said.

It was the promise of free baby-sitting that helped persuade Anna Cordrey to move back into her parents' Fremont home with her husband and toddler last year. The couple say they've become closer as a family and that their son loves the constant attention.

Still, it's a balancing act. Cordrey's parents are not always thrilled to see their grandson's bottles and toys lying around, and his bulky stroller takes up space by the front door.

"They'll be like, 'First of all, you don't need a stroller -- we didn't have strollers in Vietnam,' " said Cordrey, whose parents are Vietnamese immigrants. "It becomes a whole conversation about 'Where to put your things, Anna.' "

Ingrid Alonso, 29, who lives with her two sons in her parents' East San Jose home, said she is happy to let her parents pay the mortgage and keep house while she works on advancing her career. In addition, they are happy to help her out.

It is partly due to Latino culture, she said. "It's that traditional notion of 'What kind of woman leaves her house?' " Alonso said. "With guys, it's more like, 'Eh, he's leaving,' but with women it's like you've got to be home until you're married."

She recently went through a divorce and says living with her parents helps to stave off loneliness. She also loves her mother's home-cooked meals. However, she sometimes clashes with her father when he scolds her children.

"I like the home-cooked meals. I cooked before, but it's nice to be able to have that from the parents," she said.

Balance hard to find

Parents and children alike say it can be difficult to negotiate life under one roof. The past few years have seen a proliferation of guides from outlets such as AARP and Newsweek advising parents on how to cope with children who have not moved away.

Cleaning, financial contributions and length of stay are common points of contention.

Hodges thinks that time away from their San Leandro home did her sons good, teaching them the value of a free crash pad and the hard work it takes to pay for it. She also loves being able to keep an eye on her boys and make sure they're safe.

Her son Nick, 23, however, worries that he is missing out on his time to explore and grow.

"It's a weird balance," he said. "My mom is my biggest supporter and I have the amazing luxury of staying for free while I'm looking for a job. But I feel like I'm being contained a little bit. "

In his Oakland and San Francisco psychology practices, Coleman cautions families that an "exit strategy" with a "firm timetable" is imperative for families negotiating life under one roof for a second time.

Jaclyn Hutchins, 27, opted to move back home after graduating from college and accepting a job teaching high school English in San Ramon.

But what started as a temporary arrangement stretched on for two years. Hutchins eventually left to pursue a master's degree in the Midwest, but returned home this April to start her job search.

Hutchins would like to move out of her parents' home soon -- if only to avoid the bane of every boomerang child's existence: mom and dad checking up on where she's going or what her plans are.

However, she doesn't feel much social pressure. Like the Cordreys, she considers her position enviable.

"I think before, when the economy was stronger, people judged when you moved home," she said. "Now there's people in their 40s that are moving home -- I just don't feel out of place."

Contact Hannah Dreier at 510-262-2787. Follow her at Twitter.com/hannahdreier. Contact Paul Burgarino at 925-779-7164. Follow him at Twitter.com/paulburgarino.