This is not only a subject matter of ethics & morality, but there are laws worldwide & recently united nations also released guidelines to protect the interests of parents in the wake of increasing number of oldage homes & their starving deaths...
Following r some of the useful links to what indian Penal Code & muslim laws say...
http://wisdom.edu.ph/wishes/mod/page/view.php?id=72
http://nihfw.org/Publications/material/J322.pdf
http://dpal.kar.nic.in/.%5CAct56of2007%20PR-26.pdf
http://www.google.com/m/search?client=ms-aff-ucweb&output=xhtml&hl=en&sa=2&q=Obligations+of+children+towards+parents&site=universal
http://m.medicalxpress.com/news/2011-05-chinese-children-differ-commitment-parents.html
http://www.runelocus.com/forums/showthread.php?33840-Children%92s-legal-obligations-towards-parents-after-adulthood
Parents' responsibilities end as soon as child turns major.
http://public.findlaw.com/abaflg/flg-3-3d-5.html
I request all Gagas to get acquainted with the laws of land instead of blind conclusions with a deaf ear to morality & legality norms...