In Brazilian mathematics textbooks for primary school, toys that appear in images and text connect mathematical contents and activity with notions of gender. Based on a Foucault-inspired analysis of a corpus of 103 textbooks, it is argued that the use of toys creates a pedagogical device called a curricular-toy. This object, that emerges in the discursive practice of textbooks in the curriculum, insert children into particular binary, heteronormative notions of being boy and being girl. The gendering is legitimized by the power of the mathematical contents and activities within which gendering takes place. The curricular-toy serves as a device in the making of children subjectivities with mathematics in the school curriculum. The study contributes to current research on the cultural politics of mathematics education.