Having made many crayon quilts over the years 3 a year with a preschool I volunteered at for 12 years we have had good luck. After the blocks were colored we set the color much the way you did. The quilts are not laundered like bed sheets (regularly) they are laundered once or twice a year. Cool water, gently, with a mild detergent. They have held up well. A few of the oldest ones (20+ years) have over time faded- when they fade the owners have pulled out the crayons, re- colored and reset.