You may have admired the sculpted heads of children by Desiderio da Settignano (c. 1429–1464) in the collection of the National Gallery of Art. Washingtonians are lucky to have these pieces in their backyard, rare enough for a museum anywhere, and even luckier that the NGA is the only American venue for the first international exhibit devoted to this elusive artist, Desiderio da Settignano: Sculptor of Renaissance Florence. It draws together pieces from three major…