I had that happen when my daughter was young I ironed if off its made of wax, first I took off the loose crayon then I took paper towels and layed it over the crayon and proceeded to iron the spot changing paper to clear spots on it to absorb the crayon then I cleaned it with an upholstery cleaner when there wasnt any wax residue left hopefully this works for you. Just make sure that you do not iron on the seats directly cause they may melt.
W d 40 I heard about to try let you know how it goes
A wonderful product found at your local hardware store called GOOF OFF! It is a yellow can with a red cap. It is good stuff.