In The Chrysalids, when Aunt Harriet's body was found in the river, why is it that no one mentioned a baby?

It is in Chapter Seven where this incident is mentioned.
Aunt Harriet comes to David's mother with her new child, having lost two of her children
already because of their deviations. Finding out that her third babe too is a deviant is
too much, and thus she goes in vain to her sister to ask for her help. The harsh reproof
she receives reflects the Storm family's unthinking devotion to the creeds they profess
and show their lack of humanity, even though David's mother herself has experienced
losing children because of their deviations. Thus when it is that Aunt Harriet, now
completely hopeless, leaves them, she drowns herself and her baby, not being able to
bear another separation. The baby is not mentioned simply because, being a deviant, it
is not regarded or considered as a human being. This of course foreshadows the way that
Petra is a deviant, albeit a hidden one.