We've had a different, but related, situation with my in-laws. They retired at 55 (by choice) and started running out of money less than 10 years later. Oldest sibling (DH's brother) started subsidizing them and asked the other two siblings to kick in. We had extensive conversations about it and finally said no, because at the time, they were in their early 60s, were able bodied, and we thought subsidizing them allowed them to limp along at a time when they ought to be going back to work. Plus, it would mean signing up for it for the rest of their lives, which could be 20 to 30 years. It would have also meant saving less for our own retirement or our kids' college, and we were unwilling to do that.
Our decision is not because we are cold-hearted (I hope), but because we really didn't think it was in anybody's best interest, including theirs. We did explore other options, like providing a bit of capital to help them start a small business (think hot dog cart at the beach type thing), having them live with us for a few years and paying all their living expenses and providing a small income in exchange for child care, so they could rent their own place, bank the rental income, and not have to draw on their assets for a few years. They were unwilling to discuss any of these options, which is certainly their prerogative, but that didn't make me any more inclined to solve their problem for them by sending them money every month.
I do not believe that children necessarily owe their parents anything. I would allow a parent to live with me and make sure they were fed, etc., but I believe my responsibility is primarily to my children. My in-laws provided basic things for their kids, but once they could work (e.g., mow lawns or babysit at age 13), they no longer paid for clothes, toiletries, activities, etc. And they did not pay for college or anything that would give the kids a leg up.
As it turns out, my MIL's sister passed away last year and left her enough money to allow them to get by, and though sad at the loss of DH's aunt, I'm grateful that she was a saver and left it to her sister.