Relying on a nudge--a simple, non-paternalistic tool that spontaneously triggers behaviours in a volitional, predictable and expected way--as an education instrument, and more particularly relying on social labelling, this paper demonstrates that an extremely frugal protocol can foster children's intentions to behave pro-environmentally. In an experiment conducted among 115 children (aged between 7 and 12 years), whose gender and levels of environmental perception before the experiment were controlled for, we show that applying an 'eco-friendly' label is sufficient to trigger more subsequent intentions to behave ecologically than what was observed in the control group. We also provide evidence that the most effective age for using this nudge is above 10. Our results show that the intentions to behave ecologically persist a week after labeling. This on-going effect suggests that the influence of social labeling is not limited to the immediate response. An ethical discussion on the issue closes the paper.