Someone posed this question on the blog recently. The exact question was "who pays for assisted living the senior or the child?" Well... I have seen both. Typically, with most of the families we work with, the senior pays for their own care with their income and their assets. But I have also seen children who supplement the cost or pay for all of it. If they do, they may be eligible for a tax deduction. You would want to consult your accountant but in the meantime you can check out this article on various tax credits for seniors.
What I do know and have mentioned before is that Medicare DOES NOT PAY for long term care. It will pay for some time in skilled nursing/rehab after a hospital stay, but if your parent "plateaus" or doesn't improve in their rehab you have to start paying privately!
Medicaid does pay for senior care, but for seniors who qualify. The senior would have to have less than $2000 in assets. And when Medicaid is paying you have to go to a facility that is Medicaid certified. This of course limits your number of choices, and some places with Medicaid have lengthy waiting lists.