You love your son's drawings and treasure each picture that he colors for you -- except when those renditions are on the living room wall. Most toddlers and preschoolers color on the walls at least once. Because they have so much fun doing it, it's important to put a stop to it right away or you could find yourself scrubbing the walls every day. That's not good for your nerves or your paint. If your son does draw on the walls, sneak in a quick photo when he's not looking. After all, his pictures are still awesome even when they're not on paper.
Take the crayons, markers or colored pencils away when you catch your kiddo adorning your walls with pictures. Put them on the refrigerator or in another out-of-reach place. Tell your son that he can't color for the rest of the day because he made a poor choice by coloring on the walls instead of paper. The colors are in timeout.
Give your child a bucket of warm water and a sponge or rag and tell him to clean the walls. Even if he can't remove all of his art on his own, helping with the cleanup might deter him from doing it again. Remind him that unacceptable behavior has consequences and the consequence for coloring on the wall is that he has to clean it.
Supervise your son more closely. When you leave him alone while you go online, answer the phone or let the dog out, he's left to his own devices. His own devices being coloring on the walls. Let the dog out before your son colors so you can give him your full attention. Better yet, get down on the floor and color with him. He'll be having so much fun with you that he won't think about coloring on the walls. Resist the urge to get up and answer the phone -- that's what voice mail is for.