In the last 40 years, the family triadic processes of communication and interaction during infancy and toddlerhood have become a main area of interest in research, with a stimulating field of study growing at the crossroads between developmental and family psychology. Triadic processes were shown to be predictive of social and cognitive outcomes in children above and beyond dyadic parent-child and marital processes. New observational situations have been developed to examine triangular interactions: for example, the Lausanne Trilogue Play paradigm, which is a standardized situation designed to systematically assess how mother, father and child are able to manage triadic interactions, or The Coparental Conflict Discussion Task, that aims to assess how parents manage coparental disagreements. Specific coding systems have also been developed accordingly in order to assess different triadic processes occurring during parent–parent–child interactions.

Focusing on triadic processes allowed to highlight the parents’ capacity to coordinate and scaffold infants' social and communicative development, as well as the child capacity to regulate the family coordination thanks to its “general relational competence” or “triangular competence”. These features are cornerstones for the study of other relevant aspects of triadic functioning, such as: a) the family coordination through the transition to parenthood; b) the development of intersubjective communication in infancy and toddlerhood; c) the development of childs' sociability and social cognition; d) fathers and fatherhood in the family interaction system; e) coparenting and the quality of the interactions in diverse families (homoparental, stepfamilies, first-marriage families).

This Research Topic aims to present studies focusing on these processes, with a particular consideration for the works using observational situations, such as the Lausanne Trilogue Play paradigm, to assess the development of parental functioning and infants' social skills in a triadic research perspective. A particular emphasis will also be put on integrative researches using mixed methods, combining observational assessments with other methods, e.g. self-reported data, biological data related to parenting, neuro-imaging, or physiological correlates of parenting.

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