Sustainability is a central issue in contemporary times and has been the subject of studies and research in various fields of knowledge, including education. In our work, we sought to answer the following research questions: in what terms do primary school students have a critical understanding of what sustainability is? What dimensions are presented in the enunciation of ideas about sustainability? The analyses revealed that the students' ideas about sustainability were associated with concern for the environment. This apprehension was certainly favoured by the context surrounding the current environmental crisis. However, other dimensions, even in association, were incorporated into the understanding of what sustainability is, entering the field of complexity. Nowadays, the issue of sustainability has emerged as a topic that should be favoured in the classroom environment, particularly in order to present and discuss the aspects involved in a development model that has proved harmful to both society and the environment.