1900 census of Elliott Co., Ky, Moccasin precinct, enumerated 19 June, lists on p. 9B as family #138/141:
Cox, James E., 39, b. May 1861, Ky Va Ky, farmer; Martha, wife, 37, b. July 1862, Va Va Va, married 19 years, mother of 7 children, 6 living; Robert L., son, 18, b. Oct 1887; Minta, dau, 15, b. Dec 1884; Charlie, son, 13, b. July 1886; James E., son, 12, b. May 1888; Olvia, dau, 9, b. Mar 1891; Willie R., son, 6, b. Apr 1894. All children born Ky Ky Va.

Note that the age and birthdate are incompatible for Robert. They are both clearly legible, though. It does not say Oct 1881 or age 12.

1910 census of Elliott Co., Ky, Moccasin precinct, enumerated 3 May, records on p. 8A as family #119:
Cox, James E., 49, b. Ky Va Ky, farmer; Martha, wife, 47, b. Va Va Va, first marriage for both, married 29 years, mother of 8 children, 5 living; Willie R., son, 16, b. Ky Ky Va; James E. Jr., son, 21, b. Ky Ky Va, married, farm laborer; Mary, dau-in-law, 19, b. Ky Ky Ky, first marriage for both, married 0 years, 0 children.

1920 census of Elliott Co., Ky, Moccasin precinct, enumerated 13 Jan, lists on p. 4B as family #67:
Cox, James E., 58, widowed, b. Ky Va Ky, farmer; James E. Jr., son, 31, married, b. Ky Ky Va, farm laborer; Will R., son, 25, married, b. Ky Ky Va, farm laborer; Mary, dau-in-law, 28, married, b. Ky Ky Ky; Irland, granson, 9; Clarinda, granddau, 7; Crewel, grandson, 5; Perl, granddau, 2 11/12; Olive, granddau, 9/12; Scotland, 8, grandson. All grandchildren born Ky Ky Ky.

Scotland is the son of Willie R. Cox and Julia Stegall. The other grandchildren are the children of James E. Cox Jr. and Mary Conn.