WD-40 works well for removing crayon, as does as a product like Goo Gone. You may have some work ahead though since the heat from the dryer will have set the stain. Try using a green scotch brite scrubber pad, found on pot scrubbers in any grocer store. This pad is abrasive enough to remove the crayon without damaging the interior finish of the dryer.
Precautions:For all dryers we would recommend that you wipe down the interior of the dryer with a damp rag to remove any residue, and if you have a gas dryer leave the door open and allow it to air out for at least 24 hours before using. (This will help prevent your dryer from blowing up.)