Here's a super-simple way to recycle assorted jars and bottles into colorful vases that'll look great lined up on a sunny windowsill.
Clean glass bottle or jar
Colored sand (sold at most craft supply stores)
Cover your workspace with newspaper (this will make it easier to clean up later). Pour 1/4 cup or so of tacky glue into a plastic cup and dilute it slightly with a teaspoon of water.
Show your kids how to use a paintbrush to coat the outside of a clean bottle or jar with the glue solution and then sprinkle spoonfuls of colored sand over the glued surface, rotating the bottle to spread the sand evenly.
Allow the glue to dry completely. Once your kids get the hang of it, encourage them to experiment with multicolored designs. Or they might apply the glue in swirls or other shapes to create interesting patterns.