Human sociability is merited to highlight special attention to the understanding of phylogenies and ontogenesis, the evolutionary functions of the Homo sapiens species. Social understanding within the human context comprises of the capacity to attribute to mental and emotional states of oneself and to others. The current literature indicates potential links between children's social understanding and their peer interaction in settings of play. Nevertheless, few studies have investigated the behaviors displayed in those interactions during free play among preschool children. From the human ethological approach, playing with peers is an ecologically relevant environment for children's development; and for the observation of their social behaviors. This present study aims to describe preschool children's behaviors in terms of their social understanding abilities when they played freely in triad, and then were assessed individually on tests regarding theory of mind and emotional comprehension. The study's sample was composed of 31 typically developing children (50% girls) from low-income socioeconomic status, equally distributed in three age groups (3, 4 and 5 years old) and attending the same daycare group in Recife, Brazil. From the observation of the free play, we could identified access/receptive behaviors displayed by the children when adjusting their behaviors to those of their peer group (approach without conflict, cooperative coordinated action, exhibition, approach with conflict, intermediation, imitative coordinated action, request, invitation and offer). In result of a factorial exploration analysis, these behaviors were grouped: friendly interaction, agonistic interaction and proposal. We found age-related differences with regard to children's behaviors while interacting with their peer group in the triadic playful situation, as well as on their performances in the individual tests. 5-year-old children showed more friendly interaction than 3 and 4-year-old children, either when accessing a situation already established by others or when welcoming a new child. The older children also performed better than the younger children on the theory of mind and emotional comprehension tests. There was no relation between the access/receptive behaviors in peer interaction and children's performances on the individual conceptual tasks. The results suggest that, during ludic interaction with peers, children show an understanding of others, which allows them to adjust their action based on the interactional context. Although, children unfold and improve their understanding while interacting; interactions are both a product of and tool for social understanding; after reflecting on the psychological processes that evolved, according to the complexity of navigating within peer groups. The findings also contribute to the discussion regarding [having and using the ability to understanding others] are related competences. The behaviors categorized in this study aid the identification of children's repertoire of behavioral pat...