At what point does Desiree begin to question her child’s ethnicity?

Desiree begins to question the baby's ethnicity when she see the quadroon boy fanning the infant in his cradle.

Désirée’s eyes had been fixed absently and sadly upon the baby, while she was striving to penetrate the threatening mist that she felt closing about her. She looked from her child to the boy who stood beside him, and back again; over and over. “Ah!” It was a cry that she could not help; which she was not conscious of having uttered. The blood turned like ice in her veins, and a clammy moisture gathered upon her face.