Eleanor Jones article in thepeerage, with a link to Elizabeth Burdett’s article, is here. Elizabeth, b. some time after 1766, is dressed as a woman, suggesting this dates to around 1779. This could be, at least in part, an advertising portrait for Elizabeth.
The sheep add a note of rustic simplicity. The boy could be Frances, b. 1770, or William, b. ca. 1772.