The children were mark making using chalks, they could see the marks they were making on the sugar paper triangles.
In the Early Years Foundation Stage (EYFS), "mark making" refers to the act of young children creating marks on a surface using various tools and materials, considered a crucial developmental activity that lays the foundation for writing skills by building fine motor skills, hand-eye coordination, and creativity through exploration and sensory experiences; it's essentially the early stages of drawing and writing where children experiment with different movements and textures to express themselves.