Grandchild

Grandchild was a name used to describe one's descendant, namely the child of one's child, where the subject in question would be the grandchild's grandparent. (TV: Partners in Crime) Each subsequent generation of grandchild was given the qualifier of "great", which was then compounded. (TV: The Cambridge Spy)

Susan Foreman was the First Doctor's granddaughter. (TV: "An Unearthly Child")

As the daughter of Sylvia Noble, Donna Noble was the granddaughter of her father Wilfred Mott. (TV: Partners in Crime)

Darius Pike was the son of Harry Pike, and so the great-grandson of his grandfather William Pike. (TV: The Cambridge Spy, The Last Precinct)