Drawing upon international declarations and frameworks, such as the Brundtland Report and Goal 4 of United Nations 2030 Agenda for sustainable development, this study explores how sustainability-related content has been integrated into curricula for preschools in Italy, Norway, and Sweden. Research indicates that national curricula play a significant role in developing educational activities for young children, who will bear the consequences of inaction in the actual climate and biodiversity crisis and should therefore be empowered to effectively engage themselves towards a sustainable future. A qualitative research paradigm was used to conduct a critical content analysis to interpret and compare the differences and similarities among curricula. Although this is a curricula analysis that is based solely on secondary data, ethical considerations were also given to ensure fair representation of literature from relevant sources to avoid the possibility of bias. The results show that the concept of sustainability was integrated into all three curricula. The Italian curriculum focuses more on the sociocultural aspects of sustainability than the Swedish and Norwegian curricula. The Italian curriculum is less explicit about the need for direct contact with nature and time spent in different natural environments (learning in nature). The results are discussed in light of different national contexts. Our study contributes to increasing knowledge of national policies in preschool education in Italy, Norway, and Sweden.