First Grade Mondrian Art - from What's Happening In The Art Room... Saw a variation of this where you outline in glue to keep crayons from going outside the lines.
If you need a super simple volcano recipe, it doesn't get much easier than this. Prep is about 3 minutes, and there is no clean up necessary. Easy Baking Soda and Vinegar Volcano Eruption for Kids by Preschool Inspirations