Final answer:
During toddlerhood, children who know each other well are likely to engage in cooperative pretend play, showcasing an advance in social development and the capacity for shared interactions and roles.
Step-by-step explanation:
During toddlerhood, specifically in children aged 1-3 years, social development is characterized by significant growth in play behavior and social interactions. Based on the developmental milestones of toddlers, the correct statement regarding play is: b) Those who know each other well may engage in cooperative pretend play rather than parallel play. This is because as toddlers grow, they begin to develop the skills necessary for cooperative play, including pretend play, which is a hallmark of this developmental stage. This cooperative play may involve taking on roles, sharing, and interacting directly with one another in contrast to parallel play, where children play alongside each other but do not interact.