Nature can be very inspirational for kids. Sometimes just providing some colored paper, crayons, and glue is enough to get them involved in a project.
Using water-based non-toxic paints means the rocks will be washed clean again by the rain or you could gather rocks to paint and bring home.
They used their fingers and without my suggestion even started painting with grasses, leaves, and pine cones they found around the campsite.
If you and your kids can locate some clay or mud you could use that to mold into shapes and add some nature treasures to make designs and images.
Here’s a fun idea if you find yourself in a spot with a lot of fallen wood on the ground: Mazes using sticks.
If you happen to be in a spot with a lot of fallen wood you could help your kids create a shelter or little fort. We’ve come across some pretty fancy lean-tos and log shelters.