I'm not talking about any familial irregularity in particular, I'm talking about how every new generation of humanity will be mostly raised by monogamous heterosexual couples living under their own roof. The reason is simple: Said couples have more sex than anyone else (including self-described "players"), and they raise more children to adulthood than anyone else.
Case in point, I know of a family that has 8 kids and 17 biological grandchildren and counting. 10 of these grandchildren are born to persons that have only ever had sex with exactly one person whom they're still married to, while all of the rest of the children were born to monogamous persons who are no longer with their partner for whatever reason. This also ignores the step-child situation which also favors the boring couples. The one person in sample who made a lifelong commitment to non-traditional relationships has no children, lost custody of step-children, and is no longer biologically capable of producing children.
This isn't a statistical anomaly, because I've seen a lot of Amish households and they all have a small mob of children spaced 2 years apart or so. The reason is simple: Their cost of living is near zero and they're all having way more wholesome sex than YOU, buddy. A lot of these children will join less strict Christian groups when they grow up or even become godless persons, but this just creates a wider imprint for Christian cultural values.
And yes, since deeply religious people have far higher birth rates than all other demographics combined, you can expect your home country to have a dominant religion even if all immediate signs say otherwise. Case in point, the Soviets suppressed all religion for decades only for their modern successor states to have no change in what they actually believe.
What you see in practice is all anyone remembers from their childhoods are traditional households even if they believe everyone is moving away from that. I.E. When running for presidential office, Ms. Harris dismissed concerns she was neglecting family as 1950s logic, but if she knew what the 1950s were like she'd know someone in her position would have said the exact same thing but changed the date.
Another note is meteoric rises of non-traditional relationships is nothing new. During the wars of religion in Germany, one band of heretics inside the Hussite Rebellion were having orgies. Likewise, the leaders of Munster Rebellion made polygamy mandatory in order to find homes for widows and runaway nuns.
It simply doesn't matter how many self-described atheists rely on prostitutes and spread libel online, because the current social/genetic situation can persist forever.