Calls to tackle the global disasters of climate change and loss of biodiversity are becoming more and more prominent and urgent. Such calls require environmental citizens, that is citizens who act at local, national and transnational scales, assuming environmental agency through pro-environmental behaviours, attitudes and values in public and private spheres. To enable children to become active environmental citizens, we collaborated with five inner city primary schools in the south-east of England in co-designing a school-based, outdoor 'Wild Citizens' programme, underpinned by socioscientific inquiry-based learning, focusing on biodiversity loss. Approximately 130 primary school children (6-10 years old) explored their school grounds, discussed, decided on, and implemented interventions to enhance biodiversity, and communicated their findings within their community (schools, peers, parents, teachers). Semi-structured group interviews were conducted with a sub-sample (60%) exploring how children articulate environmental citizenship within this context. We found that environmental citizenship was articulated at both local and global scales of influence in relation to (a) environmental awareness, (b) values and (c) action competence. Children articulate the links between their performed actions to the impact these might have at a global scale, showing their ability to conceptualise and discuss implications and consequences of issues such as biodiversity loss in simple terms. Their articulation of actions as relevant and impactful to their school's grounds, transforms the issue of biodiversity loss from a slow, invisible disaster to an observable phenomenon for children, which they then act to mitigate against. This work provides empirical grounding towards the operationalisation of environmental citizenship at the primary school level in the context of a less discussed, but as urgent, ecological disaster, that of biodiversity loss.