Considering the global warming urgency, increasing the pace at which pro-environmental behaviours are learned and embraced is essential. To achieve this objective, it seems reasonable to consider children as, beyond their current and future actions, they are perceived as “change agents”. Children indeed influence close family and friends in the adoption of new behaviours. Yet, studies that consider these ‘researched’ remain too limited. This paper investigates original ways for children to learn and adopt “eco-friendly” behaviours, using social labelling. An experiment conducted among 115 preadolescents (children aged between 7–12 years) reveals that merely labelling them as “eco-friendly” is sufficient to “spill over” and trigger subsequent intentions to behave ecologically through an extremely simple protocol. It also shows that the most effective age is just above 10. Last but not least, the intentions to behave ecologically persist a week after the labelling, suggesting that children have integrated the new behaviours.