Childhood-nature experiences have lifelong effects on environmental citizenship and commitment to nature-based activities. But, it is unclear whether, and to what extent, the different mechanisms through which children and youth experience nature are associated with these outcomes. To test these associations, an online questionnaire assessing mechanisms of childhood exposure to nature, adulthood environmental citizenship and commitment to nature-based activities, and demographic variables was sent to the email addresses of 509 employees of the United States Department of Agriculture, Forest Service, Northern Research Station. The 236 completed surveys indicated four mechanisms of children’s exposure to nature. Children’s self-exposure to nature was the strongest predictor of a number of aspects of adulthood environmental citizenship and of behavioral and attitudinal commitments to nature-based activities. Exposure through school-related programs had less predictive value for these outcomes. Implications for pathways to enhance the benefits of childhood-nature experiences are discussed.