Moral philosophers in the West  hold that adult children have no more moral obligation to support their elderly parents than does any other person in the society, no matter how much sacrifice their parents made for them or what misery their parents are presently suffering. This is because children do not ask to be brought into the world or to be adopted. 

This is similar to  a case I am walking by a lake and there is a child drowning in the lake. So obviously I jump in and save her. Does she owe me any any obligation or gratitude? Why should she? After all she did not ask to be rescued.  It is  the exact same logic as the case of a child towards his or her parents. 

[That is not to say that there are no great philosophers today. On the top of my list is Kelley Ross of the Kant Fries School. A bit lower are Huemer, and Robert Hanna. Though perhaps a bit off the subject but related to the political aspect of philosophy I think the two greatest masterpieces of the 20th century were the Closing of the American Mind by Allan Bloom and The Lucifer Principle by Howard Bloom.]