Final answer:
Kendra's preference for familiar people like her aunt Sally over strangers is a developmental milestone related to stranger anxiety and represents an important aspect of her social and emotional development.
Step-by-step explanation:
The preference that Kendra shows for familiar people like her aunt Sally over strangers is considered a major developmental milestone in the field of psychology. This behavior is closely tied to the concept of stranger anxiety, which is normal and demonstrates a child's ability to differentiate between known caregivers and unknown individuals. This milestone aligns with the developmental theories of psychologists such as Jean Piaget and represents a child's cognitive and emotional growth.
Kendra's preference indicates that she has reached a stage where she is forming attachments and can recognize familiar faces, an essential part of social and emotional development. Furthermore, this kind of preference is part of a broader category of developmental milestones that includes language and communication development, self-concept, and critical stages of early childhood where autonomy is established.