Report by Kerry McCuaig, Jane Bertrand and Stuart Shanker: "Over the last few decades the science of early development has witnessed explosive growth. New technologies confirm that infancy and early childhood are the first and most critical phases of human development. A child’s earliest experiences shape the structure of genes and the architecture of the developing brain. At the same time families have changed, becoming more diverse and are raising young children in circumstances that are significantly more complex, and for many, more stressful."