Luckily, most homeowners have the products around the house necessary to remove the crayon.
These include: Baking Soda, Toothpaste, Magic Eraser, Mayonnaise and WD-40

Baking Soda
Wet a clean sponge or rag and put baking soda on it. Rub it on the crayon marks. Once the crayon is gone, wipe away residue using a clean damp cloth.

Toothpaste
Use actual toothpaste, not gel, and a toothbrush to remove the unwanted markings.

Magic Eraser
Start by getting the sponge slightly damp. Then rub the sponge on the wall and watch the crayon disappear before your eyes.

WD-40
Spray some WD-40 onto the marks and wipe clean with a rag.

Mayonnaise
Apply mayonnaise to the marks. Let it soak for several minutes. Then wipe clean with a damp cloth.