Objective: This longitudinal study examined latent profiles of parent–child interaction and their associations with triadic family interaction.

Background: A child's development is significantly influenced by early family relationships. Family systems theory emphasizes the interrelations between family subsystems, such as parent–child and parent–parent relationships, as well as the family as a whole. However, few studies have examined the relationship between each parent–child dyad and triadic family interaction.

Method: Fathers and mothers were separately videotaped interacting with their child (n = 120) at 4 and 18 months and assessed using the Parent–Child Early Relational Assessment. Triadic family interaction was evaluated at 18 months using the Family Alliance Assessment Scale within a Lausanne Trilogue Play setting.

Results: Four latent profiles of parent–child interaction were identified. Dyadic interaction that was characterized by reciprocity, positive affect, and low negativity was associated with higher family coordination. However, interaction characterized by a lack of reciprocity, negativity, and dyadic tension was related to less coordinated triadic family interaction.

Conclusions: Well-functioning parent–child interaction contributes to higher-quality triadic family interaction. In contrast, challenges in early father–child interaction, including emotional distance, a lack of positive paternal involvement, and limited mutual engagement, are linked to lower-quality triadic family interaction. Implications This study highlights the importance of supporting early parent–child relationships to promote well-functioning and coordinated triadic family interaction, and the inclusion of fathers in interventions aiming to improve family dynamics.