The present study provided some insights into the family's functioning and on the maternal and paternal differential contribution to the family's social interaction in a low-income population living in São Paulo, Brazil. The main objectives of the study were to compare mothers and fathers on their children's socialization goals (SGs) and familism (FAM) and to examine the associations between maternal and paternal SGs and FAM and triadic interactional synchronies during a family-free play session (motherfather-child). Multidimension assessments of the degree of triadic synchronies were made (interpersonal distance, visual and body orientation, play involvement, and shared affect). Differences in FAM variance scores were found between mothers and fathers, with fathers showing a greater variability in the scores, as expected. Maternal and paternal culture variables were associated with triadic mother-father-child interactional synchrony scores in different ways. Our findings suggest that fathers may have a more traditional cultural orientation in their children's SGs than mothers, and that fathers' SGs impacts the family social interaction more than mothers' SGs. On the contrary, mothers' FAM impacts the family social interaction more than fathers' FAM. In addition, the data indicates a negotiation between the parents, partially mediated by parental SGs and FAM, in the construction of the triadic space configuration, consistent with a family system perspective (Minuchin, 1985). Finally, the authors argue that an in depth understanding of the family functioning within adverse contexts will help tailor public policies centered on the family that could help buffering the negative effects of adversity.