The people the child is living with are NOT his parents.
The mother is a parent (who doesn't want the child) and the father is a parent (who does want the child). A child belongs with his parents. In this case, with his father.
(I seem to have missed if it's a girl or a boy child. I hate using "It's" to refer to a child and yet "his or her" is so clumsy. From this point on I'll have to stay with classical English where the masculine includes the feminine case)
The biological father is a guy who knocked up a woman he had known for a month, and he had no relationship whatsoever with the child. The adoptive parents went through legal channels to welcome the baby to a loving home. What the biological mother did was wrong, and she should go to prison for it, but neither the child nor his (or her, but “the masculine embraces the feminine”) adoptive parents should be punished just so that a sperm donor can get back his chattel.
Please see my post #78 and let me know if you would still give the biological father an unabridgeable property right over a child just because it was his sperm that fertilized the egg.