The 4-2-1 family structure refers to families in which three generations coexist. The '4-2-1 Problem' arose due to the One-child Policy introduced in China. '4-2-1 Problem' means that the only child will have to bear the responsibility of supporting both parents and sometimes all four grandparents in their old age. Moreover, if the only child dies before his or her parents and grandparents, there will be no one to support them in their old age.