A vital and productive society with a prosperous and sustainable future is built on a foundation of healthy child development. Health in the earliest years—beginning with the future mother’s well-being before she becomes pregnant—lays the groundwork for a lifetime of vitality. When developing biological systems occur in an environment of positive early experiences, children have a greater chance to thrive and to grow up to be healthy adults. Sound health also provides a foundation for the construction of sturdy brain architecture and the achievement of a broad range of skills and learning capacities. There is an extensive, and rapidly expanding, amount of scientific evidence illustrating the extent to which early experiences affect the biology of the body, becoming embedded in the development of multiple organ systems. As a result, the consequences of adversity early in life can be serious and long-lasting, affecting the body’s ability to, for example, regulate metabolism, fight disease, and maintain a healthy heart—as well as a healthy brain. Reducing toxic stress in early childhood is therefore an important strategy for lifelong health promotion and disease prevention.

Thanks to advances in the science of early childhood development, the chain of causes and effects in health across the lifespan have become clear. Policies and programs in both the public and private sectors can either strengthen or weaken the three foundations necessary for healthy development: stable, responsive relationships; safe, supportive environments; and appropriate nutrition. These foundations, in turn, trigger adaptations or disruptions in the body that influence lifelong outcomes in health, learning, and behavior. Understanding how each link in the chain affects the others can provide a science-based, biodevelopmental framework for decisions about policies, systems, and practices that support the healthy development of all young children, their families, and the healthy, productive adults they will become.