What is the test for determining whether or not the custody of a child is between parents?

[55] In Re Moores v. Feldstein: Whether or not the contest for custody of a child is between parents, or between a parent or parents on the one side, and non parents on the other, the paramount consideration is the welfare of the child and not the right of the parents. While the preservation of the natural tie between a child and its natural parent may be a significant factor in determining what is for the welfare of the child, it cannot be assumed, without fully considering the likely effect on the child, that the child will benefit by being returned to its mother from the mere fact of the blood relationship of mother and child. Consequently, where the mother gave up the child principally out of concern to promote her own reconciliation with her husband and not out of concern for the welfare of the child, and where the child is presently in the custody of persons who have given it loving care and attention for four years, it would not be conducive to the welfare of the child to remove her from her present home and return her to her mother. The trial judge, having found the respondent to be fit and not to have abandoned the child, erred in disposing of the matter on the basis of parental right and, in ordering the child returned to her mother, failed to have due regard for the welfare of the child.