In "Desiree's Baby" by Kate Chopin, the main character Desiree was deserted by her real family.  The theory was that her family had left her on purpose.  The family had been seen in a covered wagon crossing a river into Texas.  Desiree was about 1 1/2 years old. 

Monsieur and Madame Valmonde either literally or figuratively adopt Desiree.  When Monsieur Valmonde held Desiree in his arms, she looked at him and cried.."Dada." That was all that Desiree knew how to say when they found her.  For the next sixteen years, the couple raise Desiree as their own, particularly since they could not have children of their own.

The Valmondes really knew nothing about Desiree except that she was beautiful, kind, generous, and loving. They both love her very much.

When Armand wants to marry Desiree, Monsieur Valmonde warns him that they know nothing about her background, but Armand is too much in love to care. He marries Desiree and are happy and very much in love....until the baby is born.

When Desiree has her baby, Madame Valmonde visit Desiree and notices the features of the child.  Remember that this is her only child and now her only grandchild. She says nothing to Desiree about her thoughts.

Madame Valmonde bent her portly figure over Desiree and kissed her, holding her an instant tenderly in her arms.  Then she turned to the child.
"This is not the baby!" she exclaimed, in startled tones.

When Armand tells Desiree that he knows that the child is not white and  she is not white, Desiree is distraught.  She writes to her mother telling her what has happened.  Madame Valmonde writes her back and tells her to bring the baby and come home. Back to the place where everyone loves you for who you are. 

As Desiree leaves Armand's house, she is dressed only in her nightgown and is shoeless.  The baby is with her. She walks through the fields along the river.  The reader does not know what happens to her. Hopefully, she makes it back to her mother's home and picks up the pieces of her life.

Although seemingly unimportant, due to the scarce number of times that she appears in the story, Madame Valmonde is actually the key that hides a significant amount of foreshadowing in the story.

The wife of a well-established man, Madame Valmonde and her husband adopt foundling Desiree as their own child. The story begins with Mdme. Valmonde going to see Desiree's first child; a baby whom Mdme. Valmonde had not seen in four weeks after his birth.

In a clever play on words, Chopin clearly shows the reader that Madame Valmonde is the first person to realize that Desiree's child is different. However, Chopin downplays Valmonde's words with Desiree's own views and opinions about the changes in her baby's growth.

Upon doing a closer reading, or a second reading, of the story we realize that Madame Valmonde was not speaking about the baby's growth when she first expresses the words:

That is not the baby!

We know this because of a poignant, yet, seemingly unimportant action that may even be overlooked by the reader at first:

Madame Valmonde had never removed her eyes from the child. She lifted it and walked with it over to the window that was lightest. She scanned the baby narrowly, then looked as searchingly at Zandrine, whose face was turned to gaze across the fields.

It is clear, as it is later shown, that Madame Valmonde is the first to observe that this child is actually a black child. Why else would she need to move to the lightest part of the window to take a closer look? Moreover, why the need to scan the baby so closely, and then look straight at Zandrine, who is also black and the baby's nursemaid! Then, notice Zandrine's own expression: is she gazing across the fields because she also noticed something of which she much rather not speak?

As already said, each comment that Mme. Valmonde makes is deflected by Desiree's happy mood. As a result, Madame Valmonde may have assumed that the baby's father may have also noticed the obvious. This is the reason why she asks:

"What does Armand say?"

to which Desiree responds with positive and happy news.

As the story develops, it takes three more months for Armand to begin to detach from his child and wife. It is then when Desiree finally seems to awake form a daze and realizes that the child is, indeed, different. When Armand blames Desiree of being black (after all, she is adopted and nobody knows her ancestry), Desiree goes into a trauma that ends with her drowning herself and her child in the bayou. However, through a clever switch of situations, Chopin uses Madame Valmonde again merely to call her daughter back to their home, in order to comfort her daughter.

When a seemingly casual letter reveals that it is Armand who has the black ancestry, and not Desiree, is when the otherwise-casual actions of Mdme. Valmonde that day that she said "That is not the baby!" take a completely different meaning.