The dominant sustainability ethos and discourse within early childhood education pursue a normative ontological and epistemological direction aimed at empowering children's agency and thus, building certain predefined moral values, knowledge, and skills. Likewise, mainstream early childhood teacher education programmes strive to build early childhood pre-service teachers' sustainability knowledge and skills, especially to enhance their capacity to be transformative agents and motivators for change to engage children with sustainability challenges. In this conceptual article, drawing on posthuman concepts, I highlight the limits of such orthodox assumptions in early childhood education for sustainability (ECEfS) teacher education and invite broader ontological and epistemic possibilities. I interrogate the human-centric assumptions that unintentionally perpetuate the deep-rooted binary thinking that separates humans from non-humans and other species. In doing so, I offer an expanded understanding of the underlying ontological and epistemic assumptions within teacher education for ECEfS. I conclude by indicating how posthuman theories serve as an impetus for epistemological and ontological multiplicities in early childhood teacher education for sustainability.