Children disabled because parents have sinned

I am from a culture where people say they follow Islam, but they keep saying strange things to me which don't seem to fit in with what I am reading in the Quran. For example, one of the things people in this culture say is, if someone has a child with a disability, that child has a disability because the parents have sinned, and that disability in that child will be a punishment for the parents for the sin which they have committed in the past. I then point the following verse out to the people who have such beliefs: http://quran.com/6/164 > Say, "Is it other than Allah I should desire as a lord while He is the > Lord of all things? And every soul earns not [blame] except against > itself, and no bearer of burdens will bear the burden of another. Then > to your Lord is your return, and He will inform you concerning that > over which you used to differ." They then say to me "don't be stupid", you don't understand. So am I the one who is right or are they right? i.e. do children have to suffer because of a disability, inorder to punish parents for a sin they may have committed in the past?