My 6- and 4-year-olds LOVE these crayons. We draw pictures on our french doors every so often (spring flowers, bumble bees and ladybirds yesterday). We also use these crayons for learning/checking school spellings - nothing gets them interested like a bit of domestic graffiti.
We've had no problem removing drawings - just use a damp sponge cloth, and they're off in seconds. Highly recommended.