Simple ribbon pinwheel bow - form it around a hair clip, place stitches along each ribbon segment (shown in tutorial), then pull thread tight to cinch the bow in the middle.
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