If your relative died with minor children and a female is appointed the guardian of their estate, look carefully at her and determine who she is. If she has the same last name as the children, the likely scenario is that she is their mother. If the female guardian has a different last name than the children, she could still be the mother--except that she has married again.
It is unusual for females other than the mother to be appointed guardians of the children's estate if the father dies young. Possible, but likely.