In order to understand psychological functioning in children as well as in adults it is important to understand how the processes unfolding during brain development influence psychological functioning over the course of development. Until recently, differences between the workings of children's brains and adults' brains were poorly recognized (if they were acknowledged at all). Medieval painters captured the issue on canvas: Madonna and Child paintings in the fifteenth century often presented Mary holding a tiny mature adult man in her lap rather than an infant; the image of the infant was treated as if the child was a miniature adult.

It is now recognized that a child's brain functions much differently than does an adult's brain, but often the extent and nature of the differences between the adult's brain and the child's brain are not fully appreciated. Adequate appreciation should include recognition that children's brains absorb, perceive, process, and respond to experiences in ways that are different from the processing in adult's brains. Adequate appreciation of differences should also include understanding that much of the information held in the mature, adult brain was taken in and integrated when the brain was much less developed and, as a result, much of the information on which the adult brain relies for processing current experiences is immature in structure and activity.

With regard to psychotherapy, interventions with a child's brain call for different approaches than interventions with an adult's brain. This is due to the availability of different capacities and processes.