I found this online, but never tried it myself..Good luck!
Spray the stained area with a cleaner like WD-40. Let it soak for 5 to 10 minutes. Use a small bristle brush and scrub the stained area. Go over the area one or two times; then wipe the stain with a paper towel. The paper towel will pick up the crayon you have loosened.
Spray the area again with a cleaner like WD-40. Dab the stain with a grease-fighting dishwashing liquid. Rub this into the stain with the scrub brush. Use a wet cloth to wipe the area. The stain should now be gone. If not, repeat the process until all the stain is gone.
Allow the area to dry overnight before using the vehicle.