When grown-up `children' live at home

``Can't she pay her own car insurance, if she expects to share the family car?'' ``His room! After 20 years, can't we expect some semblance of neatness?''

``Are we feeding an entire army, or one 23-year-old?''

If any of these complaints sound familiar, then you, too, are the parent of a young adult living at home. You know the fun of keeping in tune with the newest generation of grown-ups, their fashions and fads, concerns and causes. You also live cheek by jowl with an adult newly emerged from adolescence whose wings of independence are widespread. This is a person you've known for about two decades, yet one who may have become a self-conscious stranger in many ways.

In these economically challenging times, however, the idea of young adults living at home is fairly common. With college costs skyrocketing, a student may decide to remain under her childhood roof rather than live in a dormitory, if a nearby university makes this option feasible. Now and then young people return from a failed marriage, or a young worker, finding employment at last, decides to accept the offer to stay in his old room at reasonable rent until his feet are firmly planted in the working wor ld. Even newlyweds may need shelter for a short time while establishing an independent living situation.

Loving, concerned parents are willing to help out in most of these instances.

But a variety of concerns can arise during the course of this arrangement. Talking with other parents in the same situation can be both instructive and reassuring when this happens. So can frank discussion between parents and their young adults.

It helps to take a closer look at some specific areas of concern.

Cooperation. Parents can expect young adults to be cooperative and lend a hand with domestic chores. Contributing to meal preparation, laundry, car repair, and/or yard work is something they'll soon want to do alone or with a spouse anyway. Also, consideration can be requested with regard to loud music and use of the family stereo, television, telephone, and car.

Contracts. A written contract may be helpful, if problems arise consistently with regard to house rules. (After all, it is your house.) A written contract may sound too cold and businesslike to some parents. However, it's a procedure many young people respect.

Car privileges. Young adults may share use and upkeep of the family car, with proper insurance. Of course, they provide their own gas and, it is hoped, pay their own insurance premiums. If exorbitant insurance rates for this age group are a deterrent, there's always an affordable bicycle, moped, or motorcycle and/or public transportation.

Newlyweds. Living at home is the option of last resort for newlyweds. With a little imagination and research, jobless newlyweds should be able to find an independent situation at negligible cost. How about ``house-sitting'' for a professor or other traveling professional leaving an empty residence for a semester, or a year? All the couple need pay is their own utilities. Or, they might try ``home-sharing'' with a mature single or couple struggling to stay in a large, older home. Social service organizat ions in many cities now offer lists matching students and other young adults with seniors needing help with fuel bills and chores.

Time limit. Setting a time limit on a young adult's home stay contributes much to parental peace of mind. This is a tricky one. Parents don't want to be too severe, so it's important to tread lightly but firmly. One mom and dad told their 27-year-old that they'd be happy to help out by letting him live at home until he finds steady employment. At the same time, they suggested, for his own sake, that he move into an apartment as soon as possible.

Rent. Charging young adults rent to live in their childhood home may bother parents. Yet shielding offspring from burgeoning living costs is a disservice. Young men and women over the age of 21 who have finished with school and who hold any kind of a job should pay at least token rent. (For the student who's going to graduate school or the bride-to-be saving for a wedding, a substitute arrangement might be to require substantial painting or repair work around the home or yard.) One couple co llects moderately realistic rent from their 25-year-old still using his old room. But the money is set aside in a special fund to be used only for an emergency by either son or parents. If not required earlier, his parents will give it back when he marries.