I suspect having children is like getting really drunk at one hell of a party and feeling on top of the world and making a bunch of promises to everyone, big plans and unrealistic commitments while intoxicated.
In fact the mind is hijacked by hormones and euphoria and so on to enable the whole process. Usually dirty buttholes and smelly genitals and stuff might activate a disgust reaction for one aspect of hygiene/survival, but the brain has other systems that disable it and make it arousing instead. You hear screaming children and dirty diapers and see the immense responsibility and resources required for proper child rearing and feel stress. But a dude who just blew a load into a cooch feels like a total champion and needs his trophy creature that spits out later to prove his status and suddenly is flooded with narcissistic delusions of empire building or some shit. For the woman it's similar, suddenly all that sickness and childbearing pain is worth it as she is harboring and nurturing a little miracle and she is assigned the special goddess role to bring the world the next Einstein/Brad Pitt hybrid supergod human that will cure cancer and become the ruler of planet earth that finally brings peace and solves all of mankind's problems, who also happens to break all the world records in several sports.
You get bumper stickers about the kid being a math whiz and bragging in break rooms about "oh well my kid started talking 3 days earlier than yours." It is vicarious living. Love of life by chemical means no different than a drug fiend on the streets living in a temporary feel-good delusion. They give a fuck less about the kid suffering, it's all about them. If the kid suffers, they probably see it as the kid failing them. And those are the lucky kids. There are kids who are truly unwanted and just discarded or treated like absolute shit to milk whatever benefits might come. Those parents probably don't like that the kid has reduced their quality of life and want to get as much back as possible. Narcissism in either case.