Try a crayon resist. Color lines and shapes of the artwork heavily, then cover with watercolor or paint. The waxy crayon will "pop" though the painted surface. Experiment with thinning the watercolor with water.
Experiment with crayon antiquing. Draw using heavy crayon layers to cover most of a heavy paper such as oak tag or a recycled brown paper grocery bag. Brush or dab black paint, thinned with water, over a small area of the drawing then wipe off immediately. Polish with a soft cloth or tissue. Repeat until entire piece is completed. Special effect and metallic crayons produce very handsome crayon antiquings. This technique may be combined successfully with crayon etching.