Here's a perfect activity to make use of all those little crayon stubs we invariably end up with: melt them and paint with them! Babble Dabble Do shares all the details and tips, plus ways to extend the lesson.
I love that you can achieve these gorgeous sun prints without the use of special paper. These are made on fabric with paint (use fabric paint if you intend on washing the fabric) and some pretty designs with natural objects. A little time in the sun and then you've got a gorgeous piece of fabric to play with! All the details are at Alisa Burke.
Here's a beautiful introduction to mandala making for kids! Precut tissue paper shapes designed on contact paper circles yield amazing results. Picklebums has more details and a free printable template.