This study examines how preschool teachers reflect on their role in challenging children's mathematical thinking in play. The study was conducted with participants in Italy and Sweden, and data were collected through focus group discussions. We use Pedagogical Content Knowledge (PCK) and the concept of didactic sensitivity to understand how preschool teachers describe their support of mathematical thinking in children's play and how they interact in play to promote mathematics learning. The findings show that teachers from both focus groups notice, interpret, and improve mathematical content in children's play. They outline their role in supporting mathematisation during play situations, for instance, by describing mathematical concepts and providing the children with resources. However, the findings show differences and tensions in how teachers perceive their role in children's play, with Italian teachers highlighting the importance of children's autonomy and Swedish teachers stressing the importance of being facilitators.