These instructions explain how you can get colours from natural materials. Please note that some of these require a degree of preparation.
The colours can be applied directly to paper, used to dye material (see attached picture) or used to create natural body paint by mixing them with egg white or body lotion (check for allergies),
Why not experiment with making your own paint brushes using feather, grasses or leaves attached to sticks.
Get really adventurous and make your own recycled paper [https://www.weknowstuff.us.com/2017/04/how-to-make-recycled-paper-with-kids.html]