Build the Change is a set of free online courses and activity guides for 7–12s that use building and play to explore circular design: children prototype a product, then redesign it to be reused, repaired or recycled. It is developed with the Ellen MacArthur Foundation and sits well after our ages 8–11 lunchbox lesson as a design task.
Who made and funded this: the LEGO Foundation and the LEGO Group (a toy company that itself makes plastic products) with the Ellen MacArthur Foundation. It is not a plastics-industry curriculum, but it is corporate-funded; say so to pupils and use it for the design method, not for claims about plastics. Free; link only.