Governmental organizations that do research on children or influence policy decisions:
NIMH
NICHD
Organizations that advocate for children and/or do research on children's issues:
Children's Defense Fund
Urban Institute
Child Trends
Society for Research in Child Development
MA Society for the Prevention of Cruelty to Children
Unicef
Children, Youth and Family Consortium
Organizations that are concerned with the education of preschool-aged (and older) children:
National Association for the Education of Young Children
American Educational Research Association