Much of the work on well–being and positive emotions has tended to focus on the adult, partly because this is when problems are manifest and well–being often becomes an issue by its absence. However, it is pertinent to ask if early life events might engender certain predispositions that have consequences for adult well–being. The human brain undergoes much of its growth and development postnatally until the age of seven and continues to extend its synaptic connections well into the second decade. Indeed, the prefrontal association cortex, areas of the brain concerned with forward planning and regulatory control of emotional behaviour, continue to develop until the age of 20. In this article, I consider the significance of this extended postnatal developmental period for brain maturation and how brain evolution has encompassed certain biological changes and predispositions that, with our modern lifestyle, represent risk factors for well–being. An awareness of these sensitive phases in brain development is important in understanding how we might facilitate secure relationships and high self–esteem in our children. This will provide the firm foundations on which to develop meaningful lifestyles and relationships that are crucial to well–being.