The concept of eco-citizenship is becoming more common in the literature, but little research has focused on children's perspective. This article explores the concept of eco-citizenship among 93 students of 4th, 5th and 6th grade, where they were asked to give their personal definition of "environment" and to play the role of experts in solving social and environmental problems in the context of scenarios. The analysis of individual definitions and collective solutions points to a paradox, namely a gap between the limited initial conceptualization of the environment expressed by the students in a large group whereas in the scenarios they project themselves as environmental actors. Relevance, creativity and diversity of solutions to problems show that children mobilize rich representations of the environment and eco-citizenship when they are called to act in those areas. Our study shows a strong interest in collective engagement among children, which raises questions about the role of adults and the place of the school in developing their potential as environmental actors.