Foch the Man a Life of the Supreme Commander of the Allied Armies
Clara Elizabeth Laughlin
F.H. Revell, 1919 - World War, 1914-1918
https://books.google.com/books?id=HiIFAAAAYAAJ&dq=Ferdinand+Jean+Marie+Foch&source=gbs_navlinks_s accessed 14 Nov 2018
This book says he had two sons-in-law, so we would assume that at some point he had a wife and two daughters. Sons-in-law were Captain Fournier and Captain Becourt. The book also mentions the sons-in-law had children, so General Foch must have had at least 2 grandchildren. At one point, the General played with his grandchildren at Morlaix.