Education for sustainable development is one of the key components of the 2030 Agenda. Previous research emphasizes the importance of access to education as early as possible in accordance with the goals and contents of sustainable development. It is assumed that educational policies have incorporated education for sustainable development (ESD) into key documents regulating the early childhood education (ECE), although the existence of legislation is not a guarantee that the practice follows the educational policy. Preschool teachers are key persons who can integrate content that promotes and encourages acceptance of the concept of sustainability into the ECE setting. In order to determine ECE teachers’ understanding of the concept of sustainability and contents that promote a sustainable lifestyle, an empirical study with a qualitative approach was conducted, where 91 ECE teachers from Bosnia and Herzegovina, Croatia and Slovenia participated. The participants presented their views on the socio-cultural, economic and environmental dimensions of sustainability, as well as gave many practical examples that, in their view, promote a sustainable lifestyle. They evaluated the efficacy of the researched segments of sustainability as well. Deductive content analysis was used for the analysis of the ECE teachers’ answers. In order to get a real image of sustainability in ECE practices, responses were coded using the SOLO Taxonomy and the OMEP ESD Rating Scale. The empirical study showed that ECE teachers often understand sustainability differently from that described in educational policy documents but also pointed to creative approaches to implementation.