I loved doing this in art class. Art With Mr. E: Line Design w/Shading - Grade Very cool, fun art shading project from Art With Mr. E. he's an elementary art specialist. Try this with your kids (but I think grown ups would enjoy this too).
popping paint filled balloons on a canvas . put paint tape to cover the place to stencil, put paint filled balloons around canvas, pop with darts (slingshots?), let dry, use stencil to add silhouette - love it! Or do the crayon melting thing!