Doodle's mental and physical disabilities make him dependent on others for survival and personal growth. He is mostly nonverbal and physically frail. However, he demonstrates moments of emotional depth and connection. For example, when the narrator takes Doodle for a swim in the creek, Doodle experiences a moment of pure joy and freedom, which profoundly affects the narrator.
Thus, Doodle can be seen as a partially rounded character. While his dialogue is limited due to his condition, his inner struggles and the emotional impact he has on others provide him with some level of complexity and depth.