As best I recall, Gen. Alvan Gillem had a grandson who was an officer (General?) in the U.S. Army in, I believe WW II.
I can check this out if anyone is interested.
Lt. Gen. Simon Bolivar Buckner, CSA, a friend of Gen. U.S. Grant, had a SON who was Lt. Gen., USA in WW II. He was killed on Okinamwa in 1944.