Glue crayons on a piece of white cardboard then take a blow dryer and melt the crayons. then draw a silhouette of what you want. I did this with my daughter a year ago...worked really well. I glued the crayons on first with craft glue....also have a drop sheet out as it can get abit messy!!!
This could be fun to do as art work with the middle school kids for the youth room, 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, let dry, use stencil to add silhouette - love it! Or do the crayon melting thing!