As if planning for a decent 21st-century retirement these days wasn\u2019t challenging enough for most Americans, consider the plight of the not-yet-empty nesters: According to a recent Harris Interactive poll, 40 percent of U.S. adults between 18 and 39 \u2013 thirty-nine -- who aren\u2019t students are currently living at home with their parents. It isn\u2019t just cheap or free rent they\u2019re tapping their folks for, either. The typical support package for 'generation boomerang' includes transportation costs, insurance, food and living expenses, and medical bills.\r\n\r\nAll of which has an immediate spillover effect on parents\u2019 finances:.\r\nThe Boomerang Effect\r\n\r\n \t26 percent have taken on additional debt\r\n \t13 percent have delayed buying a home or taking a vacation\r\n \t7 percent are delaying retirement\r\n\r\nMost parents, of course, don\u2019t hesitate to take on the additional burden: Another recent survey by TD Ameritrade found that 57 percent of baby boomers said they would be willing to support their adult children even if meant putting retirement plans at risk -- this at a time when 55 percent of boomers are already planning to retire later than expected.\r\n\r\nSmall wonder, then, why many couples facing this potential boomerang hit to their retirement plans need some specialized financial guidance \u2013 especially if they\u2019re still supporting 30-somethings. Following are some smart guidelines to follow from several financial planners:\r\n1. Set boundaries\r\nEnsure that you can meet your own expenses before offering to take on more. Explain to your kids how much you feel comfortable giving them and when the assistance will be cut off. Consider the financial sacrifices you\u2019re willing to make: Are you willing to take on more work? Take fewer vacations?\r\n2. Close the bank of mom and dad\r\nAdults who move back home can be expected to pay rent. Having them around may allow for some good parent-child time together, but it comes with a cost: all of your bills will creep upward. It's reasonable to ask your kids to share in the expenses.\r\n3. Be a responsible lender\r\nIf you\u2019re willing to lend children money, make it official. Write up a simple contract with interest terms and a payback schedule. This reminds \u201cchildren\u201d about the real-world implications of loans, whether those are student loans, mortgages, or credit cards.\r\n4. Dust off your financial plan\r\nIf you have been supporting your adult children, map out or update your financial plan. Discuss it with your advisor. Figure out a budget that won\u2019t jeopardize long-term goals. This may also be a smart time to update living trusts, estate plans, and wills, which most parents created when the kids were minors.\r\n5. Make it a learning experience\r\nTake the opportunity to assume the authoritative role of financial advisor to your kids. Find out how much money they think they will need \u2013 for what and for how long. Help devise their own financial plan -- which will ultimately protect yours.\r\n\r\nConsider a free financial consultation with Personal Capital today.