As with many laws, depends on the state. PA is the state with filial responsibility laws that gets the most notoriety. Anyone's best course of action is to have a thorough idea of parents' financial situation and plans for long term care.
Best info will come from:

Social Worker
Dept. of Aging
Elder Care Attorney
All in the city/state of the parents' residence

This came up in another post and got me very curious. Has anyone researched these laws? Any interesting insights? And suggested course of action? Etc.