The powdery deposit you may see on the surface of your Crayola product is called bloom. This occurs naturally and is perfectly safe.
Bloom appears on Crayola wax-based products, such as crayons and colored pencils. It occurs when oil contained in the paraffin wax used in these products seeps to the surface and re-crystallizes into a milky powder. You may also see this with sculptures made with Crayola Air-Dry Clay as the product ages or is exposed to varying temperatures and humidity. Rest assured, the crystallization is harmless and can be removed by gently wiping it away with a dry cloth.