There is a 'green gap' between environmental education policy and practice in China due to the lack of localised environmental programmes and the dominance of a lecture-based approach. In order to close this green gap, this study attempted to help elementary school children develop action competence (AC) by involving them in a water conservation educational programme (WCEP), which was designed to meet the challenges arising from water scarcity and pollution in mainland China. A total of 69 children (aged 6-8) in a Shanghai primary school participated in the WCEP for 7 consecutive weeks. The data obtained using the 'drawing and telling' approach and pre-survey revealed that the participants appeared to have superficial understanding of water, low awareness of saving water, and limited knowledge of water conservation methods before they joined the programme. The comparison between pre-survey and post-survey data indicated that the children's water conservation AC in the four aspects of knowledge, willingness, self-efficacy, and behaviour was significantly improved in a holistic way after completing the programme. Girls outperformed boys in changing their pro-environmental behaviours. The implications of improving young children's AC in environmental education in China and other developing countries are also discussed.