Parents who use guilt trip, "I took care of you for all those years and supported you now you have to take care of me!"
Big difference. Yes kids are a huge handful, can be a nightmare and put you in the poor house, but normal families (I've heard there are actually some out there) raising kids is fairly routine. Kids get smarter, learn good judgement, take care of themselves go away and support themselves. Elders who are failing physically and mentally are going the opposite direction. I'd take the terrible twos any day over dementia and dying. Should we be expected to return our parents child raising work with total devotion to their elder care? No nursing home? Gotta live with them or they with you?