There is growing acknowledgement that optimal early childhood development is crucial not only for health, well-being, and competence but also for society at large. This second paper in a series focuses on the period from birth to age 6 and draws on research from Canada and other countries to address several questions of children's development, including the following: (1) What are the known threats to young children's optimal development?; (2) Which types of targeted programs promote the development of vulnerable children and under what circumstances?; and (3) To what extend is the current approach to targeting early childhood programs consistent with what we know about what is required to promote young children's development? The paper discusses research evidence from evaluations of three categories of programs intended to promote development of at-risk children: child-focused programs, parent-focused programs, and two-generation programs. The research evidence examined clearly demonstrates that the most effective way of enhancing the development of at-risk children is through center-based, group programs. The research evidence shows that the development of at-risk children is not promoted by programs that are solely parent-focused or by two-generation programs. Following an executive summary, the paper's chapters are: (1) "Supporting the Development of Canada's Children; (2) "Identification of Vulnerable Children"; (3) "Targeted Child-Focused Programs"; (4) "Targeted Parent-Focused Programs"; (5) "Two-Generation Programs"; (6) "Universal Programs"; and (7) "Policy Implications." (Contains 232 references.) (HTH)