Having successfully experimented with depicting women in eighteenth-century costume in previous compositions such as 'The Infant's Repast,' (1848, Wightwick Manor) Brown chose to continue this theme for his first 'en plein air painting', 'Pretty Baa-lambs' . In earlier paintings he had, like other Pre-Raphaelite artists, painted the landscape outdoors but the figures in the studio. In 'Pretty Baa-lambs' Brown went further and posed his models outdoors, wanting to depict on canvas the effect of bright sunlight exactly as he found it in nature. He described working on the painting in his diary noting that
'The baa lamb picture was painted almost entirely in sunlight which twice gave me a fever while painting. I used to take the lay figure out every morning & bring it in at night or if it rained. Emma sat for the lady & Kate for the child. The lambs & sheep used to be brought every morning from Clappam [sic] common in a truck. One of them eat [sic] up all the flowers one morning in the garden where they used to behave very ill. The background was painted on the common. The medium I used was Robersons undrying copal (Flake White)' (Virginia Surtees,ed., 'The Diary of Ford Madox Brown,' p. 76).
The landscape was later retouched but a smaller version at the Ashmolean Museum, Oxford, gives an idea of its original appearance. The meaning of the painting remains ambiguous, Brown insisted that 'this picture was painted out in the sunlight; the only intention being to render the effect as well as my powers in a first attempt of this kind would allow,' however, it also combined the theme of motherhood with an interest in the eighteenth-century, both of which had preoccupied him for the previous two years ('The Exhibition of Work and other Paintings by Ford Madox Brown,' p. 6).
His second wife Emma and their daughter Cathy posed for the mother and child, and Brown hired the sheep from a local farmer.