Parents income is considered the deciding factor until the child becomes an adult and a working professional. In such case, the now adult's financial status decides whether he/she falls under Creamy/Non creamy layer. And this is assessed once in every 3 years. We cannot talk for others but for example a child's parents fall under OBC-NCL, until the child becomes self sufficient the child is considered OBC-NCL. But now if the child's income takes him/her out of OBC-NCKML bracket, he/she falls under OBC-CL by default. This is assessed duly when IT returns are filed.