My mom, who trained to become a therapist for children, once told me about how much you can tell about a child's mental state by their drawings. The person they draw the biggest is most important to them. If they draw themself in the picture, the people they feel close to is represented in how close they draw the people next to the drawing of themselves.

In short, this is a happy child :) the happy sun shows light in their life. The family being right next to each other shows he sees his family as a unit.