Co-op ideas that work for mixed ages (5-15)?

Nature journaling: every age draws at their own level. The 5-year-old draws a spider; the 15-year-old describes its predation pattern. Same object, appropriate depth.

Theatre and drama. A play rehearsed and performed gives every age a role. Older children direct; younger ones play parts.

Project fairs: each family presents something they learned in the past month. Five minutes per family. The range of topics is astonishing.

Map-based exploration games. Teams are mixed-age. The older child needs the younger one's card - genuine interdependence.