Final answer:
A toddler's declaration of "Mine!!" suggests their development of a self-concept and an assertion of autonomy, as defined by Erikson's stages of psychosocial development focusing on independence and personal boundaries.
Step-by-step explanation:
A toddler's sense of possessiveness and declarations that something is "Mine!!" is an indication that the child is asserting autonomy. When toddlers declare something as "Mine!!", it suggests they are at the autonomy versus shame and doubt stage of Erikson's theory of psychosocial development.
During this stage, toddlers are focused on establishing independence and may demonstrate their budding sense of autonomy through a variety of behaviors such as choosing their clothes or asserting control over toys and possessions. This is a crucial period where toddlers need to feel that they can act on their environment and establish personal boundaries, contributing to their developing self-concept and sense of self.