The promise to adopt must be based on some legal consideration. The absolute surrender
            of the child by the natural parent(s) or by the person or agency with legal custody
            upon a promise by the adopting parents to adopt the child is such legal consideration.
         
         However, if the contract to adopt was made some time after the child was placed in
            the care of the adopting parents, it must be shown that the surrender was then made
            absolute and permanent in exchange for the promise of the adopting parents to adopt
            the child.