Final answer:
The child's desire for a cookie despite having finished lunch illustrates 'sensory-specific satiety,' a concept from health and psychology.
Step-by-step explanation:
The scenario described where a child who has just finished eating a full lunch and a sweet dessert yet expresses a desire for a cookie upon seeing one can be attributed to a phenomenon called sensory-specific satiety. This is a concept in health and psychology where the satisfaction derived from consuming a certain type of food declines if that food is consumed continuously. In contrast, other foods not yet consumed—even if one is physically full—can still appear appealing, especially if they are high in sugar or fat like cookies.