Our married child has died. Do we, as parents, also inherit from his estate?

Yes, a mother and father remain heirs to their child, even if that child was married and had children of his own. Losing a child is a very deep grief, and the matter of property may feel awkward to think about now. But your share is fixed by Islamic law, not a sign of greed. Your son- or daughter-in-law and your grandchildren also have their own shares. If your child's spouse is raising your grandchildren in hardship, you can receive your share and then give it to them willingly. Discuss these matters gently and without haste, so the relationship with your child's spouse is preserved. See relations with the late spouse's family.