Lily, my favorite eight-year old and I played with crayons and the hair dryer yesterday.
Hot glue the crayons to the canvas (we didn't have canvas so we used paper glued to cardboard), then attack it with a hair dryer.
Lesson one - Buy cheap crayons at the back-to-school sale.
Lesson two - use a razor blade or x-acto knife to cut the side of the crayon label off or you'll be peeling little bits of paper for hours.
Lesson three - it splatters a lot so don't do it in the kitchen.
Lesson three and a half - you can get the splattered crayon off the backsplash - and the counter and under the cabinet and the stove and the counter - by warming it with the hairdryer.
Lesson four - a shower curtain liner makes a great tarp.
Lesson four and a half - don't melt the shower curtain.
Lesson five - when you aren't very tall it's best to work on the floor.
Lesson six - a heat gun might be another option because it wouldn't splatter the hot wax as much as the gale force wind from the hair dryer does. Or use a lower setting which would take longer.
But the results wouldn't be nearly as random and colorful.