This paper sets out the findings of a systematic review of the research literature on the benefits that arise when children under 12 spend time in natural environments. The review also explored the relationship between these benefits and the style of children's engagement with nature. The findings support the view that spending time in nature is part of a "balanced diet" of childhood experiences that promote children's healthy development, well-being and positive environmental attitudes and values. It also points to the value of more playful engagement styles. The findings are relevant to the development of educational planning and policy and practice, and to advocacy work.