Here's a template for your Christmas Trees, just adjust theoutline to get the style you want but don't change the inside slot positions. A dab of hot glue from a glue gun will help to stop them from folding flat together ;
How to make a whirlygig - with printable template. Could be used as a Miracle of the Sun Catholic craft
Watch the celery (or carnations/Queen Anne's Lace) soak up food coloring in this colorful science experiment: A Scientific Experiment with Celery and Food Coloring.
How to DIY Origami Butterfly- paint (watercolor?) one side of paper, text (writen/collage) on other side. Take photos of both side before folding. Hang in library/office.