Mrs. Putnam is desperate to understand why seven of her babies died shortly after birth. Her husband, Thomas, has insured her that his family, he is one of nine sons, are strong, and therefore, it is not he who has produced weak children.
Mrs. Putnam is at fault in some way for the death of these babies. She, in her misery, wants to blame someone, or something else for their deaths.
The Puritans had no knowledge of science or advanced knowledge of the body and how it works. These babies could have died from crib death, or some other cause.
The Putnams are very rich, and having only one living child left, has resulted in great despair. They are both very satisfied to learn that witchcraft was responsible for the death of their children. Each is relieved that the fault does not lie with him or her.
Mrs. Putnam, unfortunately, has her own unfortunate and sad experiences to look to for her suspicions. Her daughter Ruth has also been "afflicted" at the opening of the play, just like Betty Parris, the reverend's daughter. This had never happened to Ruth before, so there is no need for Mrs. Putnam nor her husband to believe that Ruth would be doing this to herself. Furthermore, she has no explanation for the deaths of her babies:
"...I have laid seven babies unbaptized in the earth. Believe me, sir, you never saw more hearty babies born. And yet, each would wither in my arms the very night of their birth. I have spoke nothin', but my heart has clamored intimations. And now, this year, my Ruth, my only -- I see her turning strange. A secret child she has become this year, and shrivels like a sucking mouth were pullin' on her life too...." (Act 1). Mrs. Putnam's opinion is that only a witch could cause so many horrible things to have happened in her life.