It is often interesting what people think to write on the backs of CDVs, and what they omit. The couple above are identified, in the same hand, as the Latchams, his name is not given on either card, her name is Susan (nee. Williams), and the child's name is not given at all. There is no date for the left portrait (by Mr. Thredders Royal Photographic Institution at Weymouth, England), the right portrait, obviously taken not many months later, is dated London, Thursday, November 15, 1866 (by Winter Thompson, Photographer, 137 Edgeware Road, Opposite the Music Hall). We'll never know why Susan is not in the second image. The information was likely added for family records later in the 19th century judging by the penmanship, so it is possible that the child did not live to adulthood and so was either not known or not considered of genealogical interest.
Below are CDVs from the same period of Susan's father, Thomas Williams (by Angel Photographist, Exeter) and her older sister, Mrs. Ann Berry (by W. Haddy, Brixham). The writer adds that Mr. Williams lived in Broadhampston near Totnes and was 84 years old when he died; and Susan is Cousin (Coz.) Susan, so we may safely assume a greater interest in Williams family connections. Note Mr. Williams spats.
Albumen prints of the period often lacked detail in the highlights areas.