Here's a perfect solution for all of those left over and unwanted stubby crayons. Here’s a version of how to make a new Recycled Chunky Crayon!(source, Make and Takes)
Get out your old crayons. Take off the paper (if it is still on) and break them up into smaller pieces (kids love to help with this.)
Spray your muffin tin (below is a mini muffin tin) with vegetable spray and pour some crayons into each spot. The more or less you put depends on what size you want for each chunky crayon. You can also group the crayons into colors that are fun together, red and blue for purple, pink tones or blue tones.
Place the muffin tin full of crayons into a preheated oven of 275 degrees F. I used both mini muffin tins and large muffin tins. Watch them carefully, they will melt fast. Bake them for about 7-8 minutes. When they looked melted enough, carefully and slowly remove them from the oven. You can stir them with a toothpick for a swirly look, or leave them as is. Let them cool completely (can be placed in the freezer to speed up process once the tin is not so hot.)
Once cooled, the crayons can be popped out of the muffin tin, tap the back to help this process. Then get the paper out and your ready to color.