Speaking in abstractions is nice, but the reality is that many humans create children that they are unable/do not want to take care of. These children, adopted by parents who love and cherish them as their own, should not be considered any less than bio children.
I couldn't agree with you more. Every child is a child of God and made in His image.
However, that is an entirely separate issue from how we structure our laws to best benefit children and our society overall.