Just when you thought your nest was empty...they're back. Today, it's common for adults to move back in with their parents after leaving home for college or careers. These boomerang children are adults who may not have started a job right after college or find themselves in financial crisis. They need help, so they turn to their parents.

There are more boomerang children today than there have been in nearly 70 years, says Susan Newman, Ph.D., Social Psychologist and author of Under One Roof Again: All Grown Up and (Re)Learning to Live Together Happily.

"The original concept for the book was discussing kids moving home after college," she says. "But I learned it's adult children who are in their 30s and even 40s, too."

Why Are Adult Kids Moving Home?

What accounts for the upsurge in boomerang children? Here are a few potential factors:

• Young people in their late 20s and early 30s are focusing on their careers and staying single longer, so it makes sense for them to live at home.
• The job market is tight, especially for new grads. They may not be able to afford living on their own.
• Many choose jobs where they travel a great deal and don't want to pay rent on a place where they will only stay a few nights of each month.
• Rent can be high in cities where young professionals are building their careers.
• College debt can be a burden for many graduates. Students are coming out of college with five- and six-figure debt from student loans, especially those who go on to graduate school. 
• Some adult children — including those who have children of their own — move home to save for a down payment on a house.

You might want to help your children, but welcoming them home may come with challenges. You and your spouse may have settled into new routines and discovered what it's like to be a couple again. Your adult children may also have trouble acclimating to living with you after being on their own.

How Can You Ease into the Transition?

When your adult children move back home, they are, in effect, your roommates and need to be equal partners in the household. That means cleaning, taking out the garbage, loading and unloading the dishwasher, and managing other household duties together.

One way to ensure a happy household is to migrate away from the parent/child relationship, which can be easier said than done. If you're a parent with a boomerang child, here are a few tips for you to ease — and speed up — that transition:

• Have a meeting with everyone who lives in the household. Divide chores and other household tasks equally.
• Set house rules together, but don't try to dictate how your child lives. Your child is an adult and doesn't need a curfew, for example. Work with your child to discuss guests, cleaning, and other details.
• Continue to live your own life. Head out to a restaurant with your spouse and friends instead of worrying about feeding your adult son or daughter.
• Consider asking your child to contribute financially. If they have a part-time job or are able to, ask that they pay rent or cover some of the household bills.

To create a happy household with parents and adult children, focus on respect and gratitude. Treat your children as adults, and make sure they realize you're doing them a favor by letting them move back home, likely rent-free.

"Everyone is an adult," Newman says. "Treat each other that way. It's a great opportunity to learn about each other."

If you find yourself living with both adult children and aging parents, find out more about the sandwich generation.