As a mother of 2 children, I always faced this problem of children leaving some crayon marks on the wall. But, I also felt very bad about stopping them from playing with crayons. Fortunately I found a great solution for this now...Put any white toothpaste (like Colgate White) on a damp sponge and rub it on the wall where Crayon marks are there. Your wall will be clean again. This works well on walls of most of the houses and apartments in US.