In Unwise Child the human mind is contrasted in an action-adventure setting with two alternative kinds of mentalities — the robot mind and the criminal mind. Although both alternatives have their short-term superiorities, by the end of the novel they are demonstrated to be childish in competition with the reasoning power of the mature human mind. The novel's major theme is wisdom; its minor themes are love and justice. The novel's hero, Michael Gabriel, is wise, and therefore able to love appropriately. Its heroine, Dr. Leda Crannon, is able to do likewise but only at the end of the novel. Its two villains, the robot "Snookums" and the criminal Ensign Vaneski, are incapable of wisdom or real love.

The robot mind is logical and experimental, but cannot comprehend emotionally loaded issues as the wise mind can. The robot brain, governed by Asimov's famous "three laws" of robotics (a sort of simple statement of ethical behavior for machine-minds), is in constant danger of freezing up if it is pushed too far into realms beyond straightforward research. When "Snookums" is maliciously fed a particularly potent book on theology he descends first into hysteria, then into permanent catatonia.

The criminal mind can be both clever and emotional; but, unlike the wise mind, it lacks true empathy. Vaneski is incapable of reconciling his feelings and the logic of which human minds are capable because he sees no need to do so. Being so selfish, his immediate desires suffer little inhibition from the understanding of consequences. In short, he is not only unjust, but stupidly impulsive as well. As the criminal of the novel he starts out in a powerful position, with technical knowledge, ingenuity, and his identity as a criminal concealed. But his character flaws of impatience, immaturity, and lack of humor rapidly trip him up until he loses far more than he could have hoped to gain.

The minor theme of true love is displayed in the interaction of the hero and heroine. True love has wisdom as its ally. Michael Gabriel falls in love with a beautiful young woman who is intelligent and well-educated but lacks experience beyond the narrow boundaries of her schooling and her job. Although her physical beauty is quite frankly what attracts him initially, her other fine qualities and her potential are important enough to him that he finds, with some surprise, many more noble sentiments than desire coming to the fore. Wisdom guides him not only in the choice of a love interest, but in securing her and his own happiness afterwards.

In contrast, misplaced sentiment is shown to be at best a waste and at worst a danger. The ensign and the robot are both the objects of innocently misplaced affection. The ensign uses the kindness directed toward him for criminal ends, resulting in vandalism, murder, and attempted murder. The robot has been anthropomorphized by Leda Crannon into a child-substitute. A child psychologist, she has put off getting to know real children by putting eight years of her life into a project that never had the potential to advance her in her field.