"One daughter screamed, 'You always criticized how I did my hair, and now you're criticizing how I do my daughter's hair. She has one strand of hair!'" Lewis says.

Among her patients are a couple who had been living in New York but then moved in with the wife's parents in Cincinnati. The parents no longer like her husband because they think he's not looking hard enough for a job. Sensing how her parents feel, the daughter has put pressure on her husband to find work and, not surprisingly, that has strained their relationship. To make things worse, their child is colicky, making it difficult for everyone to sleep. The woman's mother suggests she drive the child around in the car. The daughter doesn't believe that's the best way to address the issue.

The tension among the family members (as well as the crying baby), makes it unpleasant even to see them as patients. "I'm glad they only come to see me once a week," Lewis says.

It doesn't actually cost that much for children to move in with their parents. By most estimates, it's just a couple of hundred dollars a month-though that figure could rise to $400 to $500 if the parents eat out a lot and start taking their child with them. In fact, it's not the water, cable or electric bills that rise when the kids move back home. It's the grocery bill. One advisor says he had a client whose pregnant daughter and soon-to-be husband were living with them, and the client complained the couple was literally eating them out of house and home.

The cost, while minimal, can slowly erode the parents' retirement account or prevent them from putting away additional funds each month. And if they were about to move to a retirement community, those plans may get put on hold. "How much time the parents have to save must be respected by the adult child," says Guy Penn, founder of G.M. Penn Wealth Management in O'Fallon, Mo.

Penn says he worked with a couple in their mid-50s who were close to retirement when their child returned home. Those years see the parents' peak earning power, whereas the adult child has a lot more earning power ahead of him.

"As an advisor, you say what everyone knows. You're talking to educated, intelligent adults. But sometimes emotions take control and can blind people to the realities that exist on paper."

Advisors recommend charging rent-even if it's a nominal amount. Some parents give it back at the end. Others use it to defray the cost of having the child living back home.

But even more important is to manage everyone's expectations. Some advisors suggest creating a contract, complete with rules and monthly goals, outlining what will happen if the goals aren't reached. The contracts include everything from curfews and what time the child should be out of bed in the morning to household chores and who will do the child's laundry, make their meals and vacuum their room. The agreement should also have milestone markers or goals that the child must achieve each month. The parents would then meet with the child every 30 days to assure they've met those goals.

In the first month, for instance, the child should get a job-even if it's in a fast food restaurant-just to get some money coming in. But by the second or third month, he should have sent out a certain number of resumes and gone on a certain number of job interviews, lest he get stuck in the low-paying job. "You have to make sure the promises are kept, and you need written warnings, just like someone gets write-ups on a job," says Peter D'Arruda, president of Capital Financial Advisory in Cary, N.C., and host of a weekly radio show entitled "The Financial Safari."