Looks like what you suspect is right. Wonder what the R. is short for in his father's middle initial, Julius R Foster.
John C Foster
Son
United States Census, 1940
birth: 1909 Virginia
residence: 1940 Ward 3, Newport News, Newport News City, Newport News City, Virginia, United States
mother: Christian A Foster
other: Gilmor W Diggs, Madison C Bunch, William L Chaney, Russell H Setliff, Rum E Lathem
John C Foster
Son
United States Census, 1930
birth: 1908 Virginia
residence: 1930 Newport News, Newport News (Independent City), Virginia, United States
father: Julius R Foster
mother: Christian A Foster
other: Lewis Taylor, Drucella Brizendine
Churchill Foster
Son
United States Census, 1920
birth: 1908 Virginia
residence: 1920 Newport News Ward 3, Newport News (Independent City), Virginia, United States
father: Julius R Foster
mother: Christine Ann Foster