Final answer:
The formation of reciprocal relationships in children typically begins between 18 months and 2 years of age, marking an important developmental milestone in understanding others' perspectives.
Step-by-step explanation:
The question refers to the developmental psychology concept of when a child begins to form reciprocal relationships. Based on psychological research, these relationships generally start to form between 18 months and 2 years of age. During this time, toddlers become increasingly aware of others' feelings and perspectives, which allows them to interact in more complex and reciprocal ways, such as taking turns and engaging in cooperative play.