Final answer:
Children begin to show preference for same-sex playmates at the ages of 2-3 years, with a shift towards mixed-gender groups typically noticed as they grow older into the 6-10 year age range.
Step-by-step explanation:
Children begin to show preference for same-sex playmates typically around the ages of 2-3 years. At this stage, they become aware of their gender and start to understand and explore gender roles through play. Research has shown that by age two or three, most children can distinguish gender roles and often conform to culturally appropriate behaviors for their gender, such as boys playing with trucks and girls playing with dolls.
As children reach the ages of 6-10 years, they transition from playing with same-gender friends to starting to form mixed-gender groups, with friends and peer acceptance gaining importance. This progression underscores the evolving social dynamics as children develop. Although during early childhood there is a marked preference for same-sex playmates, it starts to diminish as children enter middle childhood, reflecting their increasing social flexibility and the impact of school and other organized activities like sports.