The agency to which a child has been ordered or relinquished for adoption shall be responsible for the care of the child, and shall be entitled to the custody and control of the child at all times until a petition for adoption has been granted. Any placement for adoption made by the agency may be terminated by the mutual consent of the prospective adoptive parents and the agency, or by order of the district court for removal from the home upon the application of the agency when in the opinion of the agency the placement for adoption is detrimental to the interest of the child. In the event of the termination of any placement for temporary care or for adoption, the child shall be returned promptly to the physical custody of the agency.