The outdoor space at childcare centres can be many preschoolers' primary experience of outdoor play. Trends prioritizing risk reduction have diminished access to nature and risky play. We examined the effects of an intervention to increase opportunities for nature and risky play in the outdoor play environments of two childcare centres using a repeated measures mixed methods design. We used the Seven Cs play space design criteria, adding natural materials to enhance affordances for play. We measured changes in play, social behaviour, psychological wellbeing, and physical activity in 45 children aged 2 to 5. Findings indicated significant decreases in depressed affect, antisocial behaviour and moderate to vigorous physical activity, and increases in play with natural materials, independent play, and prosocial behaviours. Early Childhood Educators observed improved socialization, problem-solving, focus, self-regulation, creativity and self-confidence, and reduced stress, boredom and injury. Outdoor play spaces are important for promoting children's wellbeing and development. (author abstract)