A commitment to long-standing child-centred ideologies and recent emphases on academic outcomes have both perpetuated narrow interpretations of play-based pedagogy in early childhood education. Instead, teachers might proactively and spontaneously deepen children's thinking and understandings related to children's own interests and motivations during thoughtful pedagogical interactions that arise from play. This paper draws on findings from a qualitative case study in Aotearoa, New Zealand where teachers used their professional expertise to engage with children's thinking and understandings. We analyse the professional knowledge, strategies and skills teachers brought to these relational and play-based interactions. We offer new conceptualising of teaching in highlighting the need to position a sophisticated blending of play, learning and teaching within participatory and relational pedagogies as a core practice of early childhood education. Further, we argue that two constructs--everyday and scientific concepts, and the zone of proximal development--position theoretically ways in which teachers' knowledge, expertise and engagement might contribute to these 'in the moment' rich, thoughtful understandings of what we term relational play-based pedagogy.