Emptying the Nest: How to Launch Your Kids Into Lives of Their Own, Instill Security and Independence, Send Them Off and Keep Them as Friends, Feel Good About Yourself Through It All, By Maryellen Walsh (Prentice Hall Press, New York) 224 pp.; $18.95

All four of Maryellen Walsh's children came back home to live for a while after they finished college. It was "perfectly fine," she writes. "Everything turned out okay . . . It is not necessarily bad or a burden for kids to come home for a while."

In fact, the more or less permanently empty nest is a comparatively new concept. Around 1900, one third of the population never married; maiden aunts and bachelor uncles -- lots of them -- stayed home. Even in 1940, 43 percent of the young people between the ages of 18 and 29 lived at home. Today's young adults who come back home to live with their parents, says Walsh, are following a tradition interrupted by the postwar generation, who became independent early.

There is a difference that Walsh does not note. The maiden aunts and bachelor uncles of yesteryear stayed at home to provide financial support or health care for aging relatives. According to Walsh, today's kids come back home because of various factors such as inflation, tighter housing, the difficulties of the job market, fear of failure and the "seductive living standard of well-to-do parents."

Most of the advice and information Walsh, an Aptos, Calif., writer, offers in her book comes from her own experience and the answers to a lengthy questionnaire she submitted to parents, about 60 of whom returned it. To her surprise, she nearly always got the same answer to the question, "What is the biggest obstacle to launching children?" The answer: parents.

Those surveyed felt that parents should begin early to foster independence in their children through summer camp, visits to relatives and summer jobs away from home. Camping out overnight in the back yard can be a valuable lesson in independence for a 7-year-old. Parents should not make a habit of rescuing a grown child. Help him out of a bind once, and then let him flounder around until he rescues himself, says Walsh, whose advice is echoed by other parents.

I think Walsh is at her best when she tackles the question of what to do if, in spite of everything, an adult offspring does come home to live, or as Walsh's daughter put it, "makes a post-college pit stop." Walsh points out that it need not be so bad; most children in their twenties are much more fun than rebellious teenagers. Half of the families in Walsh's survey had grownup kids living with them at home. Most of them enjoyed it.

She provides some concrete advice:

Agree in advance on the length of stay.

Settle how you'll handle the issues that cause trouble -- Walsh calls them "pull-aparts" -- like smoking, non-platonic sleepover guests, loud music, neatness vs. messiness, or drug use.

Expect the child to pay something, money or services or both, toward room and board.

Give up the idea of reforming a young person. Don't take in a kid to get him off alcohol or cocaine. Leave that to professionals.

Once these issues are settled, mind your own business, unless the child is about to fall off a cliff.

Walsh devotes a chapter to "When Kids Won't Launch," in which she discusses drug and alcohol problems, as well as emotional disorders. The author of a book on schizophrenia, she offers sound advice on what to do in the case of addiction or mental illness. This advice would be useful in any context, not just in the case of the still full nest.

This is a breezy, slapdash book. Forty-six of its pages are taken up with the survey Walsh sent to parents. It is, however, full of common sense and practical advice. She refers several times to an earlier book, "Boomerang Kids: How to Live with Adult Children Who Return Home" by Jean Davies Okimoto and Phyllis Jackson Stegall (Little, Brown, 1987). It has more detailed advice and longer case histories of families whose children returned home.

But for a broader, quicker and rosier overview, Walsh is best.

Ann Waldron is a writer in Princeton, N.J.