Despite the increasing prevalence of stay-at-home dads, a bad-seed novel in which a father’s insight into his child is superior to the mother’s doesn’t yet seem to exist. (Stephen King, here’s a story line for you!) It’s not just a question of who’s the primary caregiver. Rather, at the heart of this genre is a set of conventional beliefs about the relationship between mothers and children — beliefs that persist today, belying the lip service we pay to gender equality.

The most basic question these stories must address is how the child got this way. Are some children simply born evil? Or do their parents make them so, through abuse, neglect, hypercriticism or overinvolvement? Here the mother’s privileged intimacy with her child is a poisonous paradox. It’s almost always her fault in some way, regardless of her intentions. Christine Penmark learns, to her horror, that she’s the only surviving descendant of a notorious female serial killer. She was adopted as a small child and has only the barest memories of her mother, but the seed she carries sprouted nonetheless. In Gillian Flynn’s novel “Sharp Objects” (2006) — now a mini-series on HBO — a teenage girl is the killer, but the ultimate blame still rests with her mother, who narcissistically controls and neglects each of her daughters. These stories evoke normal parental fears of harming a child — passing on a genetic disease, dropping a newborn slippery from the bath — in order to take them a fatal notch further.

Then there’s the constellation of guilt particular to the working mother. That’s the heart of the conflict in “We Need to Talk About Kevin,” in which Eva is forced to abandon a career she loves as a travel writer after she becomes a mother. She observes that her son was filled with rage even as a baby — but also that when she first held him she felt nothing. Did she fail to respond to him because she sensed, even then, that he was disturbed? Or did he become sociopathic because she was temperamentally unsuited to mothering, longing for the freedom of her previous life? Less ambiguously, “Baby Teeth” suggests that the daughter is a classic psychopath who is capable of little emotional attachment and who shows no remorse for her violence. But it also depicts her mother, Suzette, as an artist whose creativity is stifled by her domestic obligations.

If we see our children as reflections of ourselves, then perhaps more frightening than their behavior is what it reveals about us. Suzette suffers from Crohn’s disease, for which her mother, who was depressed, failed to get her prompt treatment. (Again, a mother at fault.) Complications from surgery once left her with a fistula — an opening in her intestine that oozed waste and pus — which she obsessively fears might recur. Beneath our smooth surfaces, we all contain ugliness, from literal excrement to distasteful feelings we’d rather not have come to light. At one point, guilty about her joy in being temporarily relieved of her daughter’s care, Suzette presses her hand to her mouth to keep from blurting out her “unforgivable thoughts.” What parent hasn’t felt the sweet relief of dropping off a child at school or happily anticipated the end of the evening bath-books-bed routine? Part of what we fear in children is the way they are uniquely capable of bringing out unpleasant aspects of ourselves.

But the deepest fear may be the most existential: how little we ultimately understand other human beings, even our own children. “I have no clue. Who she is,” Suzette laments. That cluelessness, alas, is one of the fundamental conditions of parenting. It’s a shock to discover the inscrutability of newborn babies: We initially have no idea what makes them cry or how we can stop it. When children are little, their parents probably know them better than anyone else does, but facets of their personalities will always be mysterious. As the years go on, parenting becomes an act of giving up control, accepting that a child is an independent person, wholly separate. Whether he becomes a gardener, a stockbroker or a school shooter is ultimately not up to us. Is that a consolation or a curse?