William Cotton. A Catalogue of the Portraits Painted by Sir Joshua Reynolds, Knt., P.R.A. London, 1857, p. 49, lists the portrait of Viscount Malden and Elizabeth Capel at Cassiobury, engraved by C. Turner.
Charles Robert Leslie and Tom Taylor. Life and Times of Sir Joshua Reynolds. London, 1865, vol. 1, p. 282, record sittings for the two children in April 1767.
Frederic G. Stephens. English Children as Painted by Sir Joshua Reynolds. London, 1884, p. 81.
Algernon Graves and William Vine Cronin. A History of the Works of Sir Joshua Reynolds P.R.A. 2, London, 1899, p. 608, give an account of the sitters and a history of the picture; note that both children sat to Reynolds in 1767 and that Lord Malden also sat in 1768; suggest that the two payments (May 17, 1768, Lady Frances Coningby [sic], £175, and May 1768, Lord Essex's two children, £157 10s) indicate either that Reynolds transposed the figures or that there was a second picture.
Walter Armstrong. Sir Joshua Reynolds, First President of the Royal Academy. London, 1900, p. 218, records a sketch for the painting that belonged to the late Sir Francis Clare Ford.
A. L. Baldry. Sir Joshua Reynolds. London, , p. xxv.
W[illiam]. Roberts. "Mr. J. Pierpont Morgan's Pictures: The Early English School. I." Connoisseur 16 (October 1906), p. 70, ill.
W[illiam]. Roberts in "English School." Pictures in the Collection of J. Pierpont Morgan at Princes Gate & Dover House, London. 1, London, 1907, unpaginated, ill.
"The Cassiobury Collection." The Studio 83 (1922), p. 255.
Ellis K. Waterhouse. Reynolds. London, 1941, p. 58.
Metropolitan Museum of Art Bulletin 8 (Summer 1949), ill. p. 25.
James Parker. "A Staircase by Grinling Gibbons." Metropolitan Museum of Art Bulletin 15 (June 1957), pp. 233, 236, ill.
Malcolm Cormack. "The Ledgers of Sir Joshua Reynolds." Walpole Society 42 (1968–70), pp. 116, 119, quotes two entries: "May 17.1768 Lady Frances Coningby for Lord Malden / and Sister 175-0-0" and "May 1768 Lord Essexs two children 150 151-10".
Brinsley Ford. Letter to James Parker. November 1971, describes a copy or smaller sketch of the painting which Lord Essex gave to his great-grandfather, Richard Ford, in 1824.
Renate Prochno. Joshua Reynolds. Weinheim, 1990, p. 107, fig. 81, mentions among the artist's formats the combination of a seated female and a standing titled male, which was used again twenty years later for the portrait of Miss Mary Gideon and her brother William, Viscount Cowdray; observes that the viscount's pose was used later for the duke of York.
David Mannings and Martin Postle. Sir Joshua Reynolds: A Complete Catalogue of His Paintings (The Subject Pictures catalogued by Martin Postle). New Haven, 2000, vol. 1, pp. 119–20, no. 308; vol. 2, fig. 911, list appointments with one or the other, or both, on April 8, 9, 10, 11 (cancelled), 14, 15, and 22, on May 1, 4, 9, 12, 14, and 16, and on June 8, 9, and 14, 1767; also a sitting with Lord Malden on April 19, 1768; find the total of the two 1768 payments high, but note that Reynolds would have sub-contracted and paid for the flowers and that there is no trace of another version; call the Ford picture a copy.
Katharine Baetjer. British Paintings in The Metropolitan Museum of Art, 1575–1875. New York, 2009, pp. 19, 72–74, no. 30, ill. (color), figs. 13, 61 (installation photographs of the Great Library at Cassiobury Park).