Final answer:
The 3-year-old's statement that 'Mr. Sun goes to bed because I do' shows signs of egocentrism, a phase where children cannot comprehend that others have different perspectives and experiences from their own. This is characteristic of Piaget's preoperational stage of cognitive development.
Step-by-step explanation:
The statement "Mr. Sun goes to bed because I do" exemplifies the concept of egocentrism, which is common in early childhood development, particularly among 2-3 year olds. Swiss psychologist Jean Piaget describes egocentrism as a cognitive characteristic where the child is unable to take the perspective of others, assuming instead that others see, think, and feel the same way they do. This egocentric phase is part of Piaget's preoperational stage of cognitive development.
The scenario mentioned shows the child attributing his own experience and actions to an external object (the sun) and not recognizing that the sun's setting is independent of his own bedtime rituals. The child's development of theory-of-mind (ToM), which usually begins to manifest between the ages of 3 and 5, will eventually enable a child to understand that others have thoughts, feelings, and beliefs different from their own.
This cognitive development plays a significant role in how children interact with their environment and others, and is a fundamental concept in the field of developmental psychology.