Correlates of moderate-to-vigorous physical activity among preschoolers during unstructured outdoor play periods

► 204 observations quantify moderate-to-vigorous physical activity (MVPA). ► The physical environment during unstructured play periods supports preschoolers' PA. ► Large open spaces, gross motor manipulative objects, riding vehicles foster MVPA. ► Organizational policies and practices engaging children through teacher prompts may further stimulate MVPA.