Adoption is defined as a time when an individual or couple takes over custody of a child who is not their birth child. The birth parents have chosen to forfeit their rights and give up their children to the state. Any number of reasons for this can exist. The birth parent may want better for their child than they can give them or the childs parents may have passed away and no family members were able to or could not take the child in.
No matter the cause, the adoptive parents are the legal guardians of the child. Birth or adoptive children are not any different from each other. The adoptive parents now in charge.