To address children's loss of their father in child custody cases, Farrell wrote "Father and Child Reunion", a meta-analysis of research about what is the optimal family arrangement for children of divorce. "Father and Child Reunion's" findings include some 26 ways in which children of divorce do better when three conditions prevail: equally-shared parenting (or joint custody); close parental proximity; and no bad-mouthing. His research for "Father and Child Reunion" provided the basis for his frequently appearing in the first decade of the 21st Century as an expert witness in child custody cases on the balance between mothers' and fathers' rights needed to create the optimal family arrangement for children of divorce.