Environmental Education for Sustainability (EEfS) seeks to facilitate people’s learning about environmental and sustainability issues, not only to enable the development of fundamental scientific concepts, content knowledge and skills for understanding and dealing with current environmental problems, but also to cultivate ecological values and foster diverse competences for a responsible and democratic participation into more sustainable futures. Citizen science also focuses on engaging people with science and community action over local and global environmental and sustainability issues and topics. Defined as work undertaken by, or within, citizen communities supported and moderated by scientists and other community stakeholders, citizen science aims to advance science, foster scientific literacy and research competences, encourage community engagement and empower people to join ongoing debates about these issues. Moreover, although education and learning are not among citizen science’s first and explicit goals, there are many inherent links between it and EEfS. However, we argue that despite the many commonalities shared by the two fields, the synergies between them remain largely unexplored. This is why the approach taken by Cos4Cloud, a European Horizon 2020 project, supports the need to better understand and promote integration between citizen science and EEfS through collaborative research, technological innovation and educational design and praxis. The project builds on Citizen Observatories (COs), i.e., technological platforms and tools that facilitate the development of citizen science projects, particularly those whose main objective is large-scale citizen participation, by digitally connecting citizens, supporting their observational competences and providing information flows. Among its ambitions is to develop a minimum viable ecosystem for participating COs and a set of co-designed services that will enable the networking of citizen observatories and provide a synergetic benefit for all stakeholders. Once ready, these services will be uploaded to the European Open Science Cloud (EOSC) as modules, so that any CO can select and install the ones it needs. A second goal is to broaden the current scope of citizen science based on COs through their integration into school based EEfS and create more opportunities for testing their integration and the new services in terms of the experience they offer. In this paper we first outline the general strategy developed to support the goal of integrating the project’s CO technologies into school-based EEfS. We further illustrate this approach through a case study designed to engage Greek primary school children with two citizen observatories, Pl@ntNet and OdourCollect, as educational tools with added value in a school EEfS project. A new-materialist approach was chosen, building on children’s encounters with their more-than-human local environments and the intrinsic value of nature, while exploring biodiversity and environmental quality and highlighting various threats to their environments’ ecological balance. Finally, we report findings from a study conducted to investigate the experience developed in children from their mediated and immediate engagement with their more-than-human nature world. We argue that technology can become an important non-human agent in experiencing and learning ‘childhoodnature’ and offer new perspectives to both citizen science and EEfS.