Through his oldest son Friedrich Franz III he is the grandfather of:
Friedrich Franz IV Grand Duke of Mecklenburg-Schwerin
Alexandrine, Queen of Denmark
Cecilie, Crownprincess of Germany and Prussia
His oldest daughter Marie:
Grandduke Cyril Wladimirovich of Russia pretender to the Russian throne. His granddaughter is the current head of the Russian imperial family and other offspring include the head of the houses of Germany/Prussia and that of Leiningen as well as members of the Serbian royal family.
Elena Wladimirovna, princess Nicholas of Greece and Denmark parents of
Olga => married to Paul regent of Yugoslavia
Elisabeth married into a German dynasty
Marina => married to the Duke of Kent
His younger daughter Elisabeth became Duchess of Oldenburg
His youngest son Henry became prince of the Netherlands and fathered Queen Juliana of the Netherlands.