This flag was given to my grandfather Millard Fillmore Green during WWII. He had four sons serving in the military and all of them served overseas, in combat.
"Son's in Service" or service flags were given to families who had members in the military.
The military directive for them reads: "C10.3.4.1.1.1. The number of blue stars shall correspond to the number of Service members from the "immediate family" who are symbolized on the flag."
Sec. 901. - Service flag
Individuals Entitled To Display Service Flag. - A service flag approved by the Secretary of Defense may be displayed in a window of the place of residence of individuals who are members of the immediate family of an individual serving in the Armed Forces of the United States during any period of war or hostilities in which the Armed Forces of the United States are engaged.
He should have received another one with a gold star after his son Bryant was killed in 1943 but he never did.
The directive says the flag was only to be displayed during a period of war. My grandfather never took his down. This one was on his living room wall the day he died in 1973. I'm not sure if he considered himself still at war. He was never a big fan of some of the social and legal changes that happened in the South of 1950s and 60s so maybe he was.