The purpose of this article was to explore the potential application of the science of complexity to aspects of team, family and group systems. A child and adolescent mental health Day Program as a tightly knit multidisciplinary team closely interacting with family systems, provides an opportunity to illustrate concepts of this general scientific framework and offer potentially unique insights. In particular, the relevance of diversity and interconnectivity between parts of a system are highlighted. Ideas explored include team functioning, how change occurs in families and new ways of looking at groups. Furthermore, complexity provides support for intensive multisystemic interventions such as the Day Program to assist families with severe and chronic child mental health issues.