Skip to my Lou is doing a super fun 30 Day Craft Camp...you should DEFINITELY check it out...I don't have 30 days of crafts, but here's a fun one we've done at our house...huge kudos to Jean for teaching us this SUPER easy way to do this (we used to color first, THEN heat...this is WAY better!).
First off...you'll need some flat rocks on a cookie sheet. Preheat the oven to 425 degrees and heat the rocks for about 10 minutes.
Peel paper off the crayons.
Then place the hot rocks on a paper towel...warn your child(ren) NOT to touch the rocks...they are HOT. The crayons will melt as they draw.
Once they are done let them cool and buff them with a cotton cloth to make them shine.