In recent times, Australia has recognised and enacted a range of initiatives at service, system and community levels that seek to embed sustainability into the early childhood sector. This paper explores the impact of a professional development (PD) session that provided opportunities for early childhood educators to learn and share ideas about the theory and practice of sustainability generally and early childhood education for sustainability (ECEfS) specifically. The PD was entitled "Living and Learning about Sustainability in the Early Years" and was offered on three occasions across Tasmania. A total of 99 participants attended the three PD sessions (one 5 hour; two 2 hour). The participants had varying levels of experience and included early childhood teachers, centre based educators and preservice teachers. At the start and end of the PD, participants were invited to complete a questionnaire that contained a series of likert scale questions that explored their content knowledge, level of understanding and confidence in regards to ECEfS. Participants were also asked at the start and end of the PD to "list five words you think of when you consider the word sustainability." A model of teacher professional growth was used to conceptualise the results related to the changes in knowledge, understanding and confidence (personal domain) as a result of the PD related to ECEfS (external domain). The likert-scale questions on the questionnaire revealed significant positive changes in levels of knowledge, understanding and confidence from the start to the end of the PD. Differences as a function of length of PD, level of experience and role are presented and discussed. The "5 words" question showed that participants widened their understandings of ECEfS from a narrow environmental focus to a broader understanding of the social, political and economic dimensions. The early childhood education and care (ECEC) sector has been characterised as having a pedagogical advantage for EfS suggesting that early childhood educators are well placed to engage with EfS more readily than might educators in other education sectors. This article argues that PD is necessary to develop capability in educators in order to meet the imperatives around sustainability outlined in educational policy and curriculum documents in ECEC.