https://www.osv.com/Article/TabId/493/artmid/13569/articleid/16977/Default.aspx

Apart from joint biological parenting, it also didn’t matter very much whether the parents were same-sex or opposite-sex. I compared opposite-sex parent families in which only one parent was a biological parent — think step-families — or neither parent was — think adopted children — to their same-sex counterparts, and found no differences in child emotional problems.

There is no evidence, in other words, that the quality of parenting, parental support, parent-child dynamics, etc., are less beneficial for children with same-sex parents than for those with opposite-sex parents, when those parents are not their natural mother and father. The point is not that same-sex persons, whether married or not, are not somehow less loving or effective as parents, but that, unlike opposite-sex partners, they cannot jointly procreate a child, which is the type of natural relationship in which children thrive best, by far, with regard to emotional health.