The primary benefit of marriage for children may not be that it tends to present them with improved parents (more stable, financially affluent, etc., although it does do this), but that it presents them with their own parents.

This is the case for 98% of children in nuclear families—which most successfully fulfill the formal civil premise of marriage, that is, lifelong and exclusive partner commitment—compared to less than half of children in any other family category, and no children in same-sex families.