As part of a series of reports designed to support the implementation of Proposition 10: The California Children and Families Act and to provide comprehensive and authoritative information on critical issues concerning young children and families in California, this report reviews the research about early childhood brain development, examines the extent to which parents are aware of the importance of early childhood for brain development, identifies known risk and protective factors for cognitive and social-emotional development, and describes interventions that have been shown to support development in these areas. The report concludes by asserting that four findings emerging from neurobiology and psychology--that a child's brain is immature at birth, that it is changed by experience, that the timing of experience can be important, and that relationships influence a child's social and emotional functioning--have important implications for parenting and public policy. The report's two appendices graph the developmental course of human brain development and delineate risk factors and developmental outcomes. (Contains 93 references.) (KB)