The earliest years of one's life are crucial in many ways, including how they set one on paths leading toward--or away from--good health. Family income, education, and neighborhood resources and other social and economic factors affect health at every stage of life, but the effects on young children are particularly dramatic. While all parents want the best for their children, not all parents have the same resources to help their children grow up healthy. Parents' education and income levels can create--or limit--their opportunities to provide their children with nurturing and stimulating environments and to adopt healthy behaviors for their children to model. These opportunities and obstacles, along with their health impacts, accumulate over time and can be transmitted across generations as children grow up and become parents themselves. This brief, is one in a series of twelve on the social determinants of health, and answers questions on children's health and development including: (1) How do social and economic conditions early in life shape children's health and development, thus shaping adult health?; (2) How strong is the evidence connecting early childhood development programs with health?; (3) Successful early childhood development programs often have been multi-faceted. Do we know what specific components work?; and (4) Investing in early child development to achieve America's health and economic potential. This issue brief is one in a series of 12 issue briefs on the social determinants of health. (Contains 1 figure, 2 tables, and 4 resources.)