Can grandchildren inherit if their parent (the deceased's child) died before the grandparent?

This is one of the most commonly misunderstood scenarios in Islamic inheritance, and the honest general answer is: not automatically, and not through the fixed fara'id shares in the majority classical position — if a son or daughter dies before their parent, that predeceased child's own children (the grandparent's grandchildren) do not step into their deceased parent's fixed share the way they might expect under, say, general Indian civil succession concepts. Whether and how much a grandchild receives depends heavily on which other heirs survive (for example, whether the deceased grandparent left other living sons), which is exactly the kind of case-specific calculation this page does not attempt to resolve in the abstract.

Because this scenario so often produces outcomes families find surprising or unfair — a grandchild potentially receiving little or nothing from a grandparent's estate despite their parent's earlier death — many contemporary scholars and Islamic bodies, and Indian legal frameworks discussing "representation" for orphaned grandchildren, actively recommend that grandparents use the discretionary one-third wasiyyah (see Q3 and Q11) specifically to provide for grandchildren in this position while they are still alive to do so. If this situation applies to your family, treat it as a priority to get an actual fara'id calculation done by a scholar or Islamic inheritance calculator, and to discuss a wasiyyah with the grandparent while possible, rather than assuming any general rule of "representation."

Source: general Sunni fiqh (fara'id) on the exclusion of grandchildren by a living closer heir in many configurations; see Islam Question & Answer and Islamweb fatwas on grandchildren's inheritance, and contemporary scholarly recommendations to address this through wasiyyah.