Image: Teen sleeping in class © Image Source, Getty Images

You or someone you know probably has an adult child living at home, according to a "60 Minutes" and Vanity Fair poll. More than half, 54%, of today's parents say there's no set time when kids should stop living at home -- not when they graduate from college or get a full-time job, or even when they get married. More and more college-age and post-college-age children are taking advantage of this and living at home.

Forty percent of American adults ages 18 to 39 either live at home or have done so recently, according to a poll for the National Endowment for Financial Education. That's alarming, as the findings exclude students and include "kids" up to the age of 39. The same survey found that these adult children are having a financial impact on their parents, too. Of the surveyed parents with adult children living at home, 26% have taken on debt to support their kids, and 7% have delayed retirement.

This begs the question for the 46% of parents who think kids should live their own lives at some point: When should you cut the financial cord?

Start early

Children should begin earning for themselves at an early age by contributing to household chores and taking on extra tasks to earn cash, says family finance expert Ellie Kay. Make sure children understand their responsibilities, and have their contributions increase as they get older.

"If you set a precedent that you will just hand over cash every time kids ask, the problem can exacerbate as adult financial responsibilities and mistakes take over," she says.

David Bakke, a personal finance reporter, says his parents had a rule: If he wanted to buy something, he had to earn the money to pay for it. Today, he says it's "one of the best things my parents did for me."

This rule also applied to Andrew Schrage, one of Bakke's reporting colleagues. Schrage's parents made him save up for a car as a teen, "although they did sell me one of their old cars at a significantly reduced rate and (paid) for my auto insurance into my late teens," he says.

Kay agrees that if a teen wants to drive, the child should pay for his or her own car. She also thinks teens should be required to pay for a portion of their auto insurance so they appreciate what it costs.

The entitlement generation

An attitude of entitlement is especially prevalent in kids who are not used to earning their own way and have no idea what items cost, Kay says.

"As parents, we owe our children food, clothing, health care and shelter, not fun with friends, designer clothing, cellphones with data plans, a car or a party-school college experience," Kay says. "If kids want those things, they need to earn it for themselves. Otherwise, they feel entitled instead of appreciative."

She emphasizes that when kids work for things, they value them more. And that includes a college education.

Students who choose to work to contribute a moderate amount toward their college expenses often do better academically, according to the College Board. Two-thirds of full-time undergraduate college students receive some type of financial aid. About 61% of that aid is in the form of grants, scholarships, federal work-study, tax credits and deductions that do not have to be repaid. The remaining 39% of financial aid dollars consists of loans.

Start cutting the cord on college financing early. Kay says teenagers should know a portion of their time must be spent working toward money for college. This includes attaining a high grade-point average and excelling in extracurricular activities. In addition, researching local, affordable schools; applying for state scholarships, grants and work-study programs; or joining the military are all ways to reduce college costs and earn money for tuition and living expenses, Kay says.

She adds that the goal is to raise adults who take responsibility, because the period between ages 18 and 22 is when a parent should start ending most forms of financial support.

More from Bankrate.com: