I have not found Irena in the 1860 census as a child.
Census Notes for Henry M. & Irena ("Rena") (Family)
1870 census of Floyd Co., Virginia, Indian Valley & Burks Fork district, enumerated 27 Aug, lists on p. 29 as family #190/178:
Duncan, Henry M., 28, farmer; Irena, 24; Ambrose, 2; Sarah J., 1; Duncan, Polly, 30, without occupation. All born in Virginia.
1880 census of Floyd Co., Virginia, Indian Valley district, enumerated 4 June, lists on p. 9 as family #73/74:
Duncan, Henry M., 28, farmer; Irena, 24, wife; Ambrose, 11, son; Sarah J., 8, dau; Betsy, 7, dau; Albert B., 5, son; Luvina, 4, dau; Analine, 2, dau; Polly, 44, sister. All born Va/Va/Va.
It is odd how Henry and Irena are recorded with the same ages in 1870 and 1880. Judging by the 1890 census, they should probably be in their thirties in 1880, but the ages clearly say 28 and 24.
1890 census of Floyd Co., Virginia
14, lists in Indian Valley district:
Duncan, Henry M., 49; Irena, 47; Albert S., 17.