The Donna Reed Show
A Way of Her Own
S5 E20:
A little girl named Trisha follows the Stones home from the park and says that she is one of the family. After a long effort to find her real parents,her uncle arrives. He realizes that the orphaned Trisha loves being in a family and that the Stones are fond of her. He arranges it so Trisha can stay with the Stones. Thus a new family member is added.