One of the things I enjoy most in life is spending time with my 7 year old son drawing. We draw everywhere and anywhere. For him, it's an extension of this fantasy world in stories that he creates with my wife and I, where each of us acts out different characters. Sometimes we do it with action figures, other times with character cards (Pokemon), with drawings we create, or just walking around telling stories out loud.
I love the story telling, but what I really enjoy most is when we create these characters on paper. One thing I've always done with him is to show him characters in different states of emotion, sometimes putting them in comic strips. The simple way is through the eyes and mouth. A drawing teacher I once had, who taught Manga cartooning illustrated this clearly to me, and I passed it to my son.
One day, he was telling stories with this Ugly Doll, named Chuckanucka, and through the story the character went through several emotions. He started showing them by doing the lines we use over the eyes using his fingers. I thought that was pretty cool.