Why are the Putnams so eager to assume that the children are ill because they are bewitched?

Explanation:

In The Crucible, the Putnams have lost seven children with an eight, Ruth, very sick. They think this to be very unusual because it is just too many children to have died from the same illness.

Mr. Putnam rules genetics out as a factor by referring to the large family he came from where he had ten brothers which meant to him that his genes were strong enough for his children to stay alive.

Another reason was the need to blame the deaths of the kids on something especially for Mrs. Putnam who kept seeing her children die. She needed to blame something to feel better and witchcraft was an easy factor.