Children progress through different stages of peer relationships as they develop. Solitary play occurs first as infants play alone, followed by parallel play where children play side by side without interaction. Associative play emerges as toddlers engage in independent play but join others briefly. Cooperative play involves working together to accomplish goals through constructive or symbolic play. As social skills develop, children learn to enter group play through observation before joining. Aggression is common in young children but physical aggression declines in preschool while indirect aggression increases from preschool to age 11. Parental influences like reinforcement, modeling, and positive statements impact children's social and prosocial behaviors.