I bought these Crayola window crayons MONTHS ago. They have the consistency of some crayola pastels I've had for years and they clean off glass in a cinch.
It took Daughter a LOT of convincing that it was ok to color on the glass doors because for so long she's heard, "crayons are only for paper." Finally, she believed me that these were special "glass door crayons" and she was not going to get in trouble.
Behind her you can see almost see the art she drew on the door ... and all the smudges she/we made in the process. She's also holding up the picture she drew when she tired of the glass.
She loves to use crayons, markers, colored pencils, chalk, pastels, paint. pretty much anything I'll let her use. I love that she can draw circles now ... even though they look mostly like hearts.