Hold a pencil eraser gently against the crayon marks. Alternatively, press a steel wool soap pad against your wallpaper.
Rub the eraser or steel wool up and down against the crayon marks. Be careful not to rub it against the wallpaper: Your goal is to angle it so you just keep it on the wallpaper.
Blow lightly on the walls to remove the flaking off crayon marks as you go. Continue to run the eraser or steel wool lightly against the crayon marks until they begin to fully vanish.
Run a hand-held vacuum cleaner over the walls and floor, sucking up the dust from the crayon marks.
Moisten a soft cloth with some lighter fluid. Alternatively, dab a soft cloth in some mayonnaise.
Rub the lighter fluid- or mayonnaise-saturated cloth against the crayon marks. Allow the substance to penetrate them for three to five minutes.
Rub the cloth against the stains until all the marks are on your cloth and off the wall. Once the marks are gone, wipe the wall clean with a damp cloth.