Just use a little...

Ethan drew on his sisters wall. When it was pointed out to me he quickly said, "Don't worry, I will clean it," and went off for a washcloth. He soon found out that a wet cloth does not get ink off. "What am I supposed to use?" he asked. I told him, "Elbow grease...go ask Dad if he has some." He replied, "That's okay, I'm using mine," and began rubbing his elbow with the cloth. Funny thing...elbow grease doesn't get ink off either.