Mom and Dad Living with Grandma and Grandpa

7.7 U.S. children are living with grandparents and 8 in 10 of those children have at least one parent also living with them.  Guests are like fish.  They stink after three days.  Though this may be a good short-term solution for young parents to find their financial footing, it can be a drag on grandma and grandpa's retirement and retirement nest egg.