It's not always bad to think negatively. Step away from the everyday drawings that focus only on positive space, or the objects occupying a space, and try your hand at negative space drawing. Negative space is the area between objects. If you mix the two types of spaces together, you can end up with a neat and unique piece of art.
Spend a few minutes researching examples of negative space art before you and your child get started. A quick internet search will provide tons of examples. Try focusing on letter art that utilizes negative space.
Help your child brainstorm ways to use negative space based off of the example you both have studied. If he's stumped, consider doing a simple negative space trick: draw a word using bubble letters, but "leave out" every other letter. For example, in the word cat, the first and last letter would be drawn, but the "a" would be absent. The "a" will be revealed through negative space. (If your kid wants some practice sketching bubble letters, have him check out How To Make Bubble Letters.)
Have him draw his negative space art on a sheet of paper. With letters, make sure the edges touch.
If he makes a mistake, just take out another piece of paper. With negative space drawing, it's all about practice!
Remember that some letters are harder to draw with negative space than others. If he gets stumped on a letter, have him rearrange his word to accomodate that letter with postive space.
When he's done, have him show off his art to his friends and family members. Can they read his letters?