Final answer:
Children frequently begin to show a preference for same-sex playmates at age 2-3, which becomes more established by age 4-5 as they learn and adhere to societal gender roles.
Step-by-step explanation:
Children begin to prefer same-sex playmates predominantly between the ages of 2-3 years. This preference is observed as part of their developmental process where they become aware of gender roles and start forming gender-based preferences in socializing and play. According to cross-cultural studies, by the age of 4-5, most children are already well established in culturally defined gender roles.
These behavioral patterns are strongly influenced by how society shapes gender socialization and the types of toys and activities children are encouraged to engage with. Children learn these gender roles through interaction with their environment and reinforcement of gender normative behavior by their caregivers and society at large. In later years, specifically from the ages of six to ten, children's social groups broaden to include mixed-gender groups, reflecting a developmental shift towards more inclusive social interactions.