Well, I don't think I'd use the Crayola washable markers to mark a quilt, especially a very light colored one.
I tested 8 colors and ironed half of the test strip to see if heat makes them more permanent. Washing by hand in cold water, *most* of the color came out but there are definite blobs of color left even after a pretty vigorous scrubbing.
Ironing didn't seem to make any difference. Orange and purple washed away the best and red and blue stayed the most.