"I am sometimes asked up to what age do these principles apply. The answer is debatable, but I would say anytime up to the age of, say, 99."
Proposition 1. In order to develop--intellectually, emotionally, socially, and morally--a child requires participation in progressively more complex reciprocal activity, on a regular basis over an extended period in the child's life, with one or more persons with whom the child develops a strong, mutual, irrational, emotional attachment and who is committed to the child's well-being and development, preferably for life.
Proposition 2. The establishment of patterns of progressive interpersonal interaction under conditions of strong mutual attachment enhances the young child's responsiveness to other features of the immediate physical, social, and--in due course--symbolic environment that invite exploration, manipulation, elaboration and imagination. Such activities, in turn, also accelerate the child's psychological growth.
Proposition 3. The establishment and maintenance of patterns of progressively more complex interaction and emotional attachment between caregiver and child depend in substantial degree on the availability and involvement of another adult, a third party who assists, encourages, spells off, gives status to, and expresses admiration and affection for the person caring for and engaging in joint activity with the child.
Proposition 4. The effective functioning of child-rearing processes in the family and other child settings requires establishing ongoing patterns of exchange of information, two-way communication, mutual accommodation, and mutual trust between the principal settings in which children and their parents live their lives. These settings are the home, child-care programs, the school, and the parents' place of work.
Proposition 5. The effective functioning of child-rearing processes in the family and other child settings requires public policies and practices that provide place, time, stability, status, recognition, belief systems, customs, and actions in support of child-rearing activities not only on the part of parents, caregivers, teachers, and other professional personnel, but also relatives, friends, neighbors, co-workers, communities, and the major economic, social, and political institutions of the entire society.
From: "Discovering What Families Do," by Urie Bronfenbrenner in Rebuilding the Nest: A New Commitment to the American Family, published by Family Service America, 1990.