Monogamism prevalence is vey high, although not universal. There are rare matriarchal societies (matrilocal/focal, to be exact), where the "clan" is based on the offspring of one woman. Mating occurs between poeple of different clans and children are raised in the mother's clan, by their mother, aunts and uncles.

But even there, ideed, the children know who their father is, even though they don't have a peculiar relationship with him.