There has been a major international focus on the education and care of toddlers. To date, empirical studies on adults' interactions in play with toddlers have focussed on the proximity of teachers, teachers' affective responses, and joint attention between adults and children in play. However, less attention has been given to the role of two teachers working together in supporting children's exploration of concepts in joint play. This paper takes a cultural-historical perspective and draws upon the concepts of play and subjective positioning to investigate how co-teaching promotes toddlers' joint play and exploration of mathematical concepts. Visual data of a group of toddlers playing with two teachers is analysed to explore how the teachers applied co-teaching pedagogy to support children's exploration of mathematical concept. The study argues that co-teaching provides potential to support collective play as two teachers can work collaboratively to address the toddlers' challenges and needs and support their exploration of the rules and mathematical concepts in play. Co-teaching by paired teachers enables toddlers' joint play to become more complex, helping the children to explore mathematical concepts and, in turn, further enhancing their play.