So I haven't read Engels' The Origin of the Family, Private Property and the State yet and it goes more into it, He touches a bit on this concept in Principles, iirc.

The concept of a traditional marriage is basically one where the man is the head of the household. As such it is another arm of the patriarchy. In a traditional nuclear marriage, the husband usually has the say in anything, is expected to be the one that makes the most money, and historically before the economy shifted away from a one income household, was expected to be the one who works while the wife stayed home and cleaned, did laundry, fed the kids, etc.

In homesteading era of the US, families had a lot of kids. This had 2 main reasons. The first was to combat the child mortality rate of the time so the family lineage could continue. This is why it's so important for these families to have a good strong male child. The other reason is to have a pool of labor. Most homestead families, pioneer families, and even in the Amish families in the States, use their children as free labor.

Traditional or nuclear families are also sexist//misogynist, as the wife will generally have a lot less say in matters, was not expected to work for an income, and was historically considered as the husband's property. Same for the children. In a sense, the family below the husband were simply viewed as assets, and exploitable labor.

I should mention, I am not against a normal unity(one man, one woman, and kids should they choose). I am actually in one myself. She has historically made most of the money, and I am the one that generally does all the cleaning, however. We approach our marriage without defined gender roles and we also make decisions democratically. As our kids are getting older, we also ask them for input gradually. For example, and it's a smaller, silly example, but we are allowing our oldest to help plan for weekly meals that I make, to give him a bit more "voting power" so to speak. As he gets older, he will get more say in things.