This article explores how a bilingual preschool teacher creates mathematical preconditions and socio–psychological premises that advance children’s understanding of mathematical concepts, and considers factors such as language and materiality that influence mathematical activities in a multilingual Swedish preschool. Elements of situation theory (devolution processes) and of actor-network theory (materiality as mediator) interact. This article highlights whether some didactic contracts promote interactions between materiality and multilingual children in two mathematical activities, one planned and controlled by the teacher to introduce the concept of shapes and the other spontaneous, in which the teacher follows the children’s desires.