Thesis to opt to the degree of doctor in psychotherapy / The prevalence of social-emotional problems in early childhood continues at a high level (Centro de Microdatos-Universidad de Chile, 2014). This stage is a critical period in which the immediate family is the most influential system in childhood development (Bronfenbrenner, 1987). Conversely, the parental reflective function (RF) is considered a protective factor in early parenting (Stacks et al., 2014), assuming a relevant role in socialemotional development in early childhood (Ensink, Bégin, Normandin, & Fonagy, 2016; Smaling, Huijbregts, van der Heijden, van Goozen, & Swaab, 2016a). Objective: To describe and analyze the relationship between fathers’ and mothers’ RFs, the quality of the mother-father-child triadic interaction, and children’s psychomotor development and social-emotional difficulties. Method: A non-experimental, transversal and correlational study was developed. Fifty mother-father-child triads, each in a current relationship that included at least one child from 12–36 months of age, were evaluated. Sociodemographic background, triadic interaction (LTP, Fivaz-Depeursingue & Corboz-Warnery, 1999), parental RF (PDI-S, Slade, Aber, Berger, Bresgi, & Kaplan, 2012, assessed by RF Scales, Fonagy, Steele, Steele, & Target, 1998), psychomotor development (ASQ-3, Squires & Bricker, 2009) and social-emotional difficulties (ASQ SE, Squires, Bricker, & Twombly, 2002) were measured. Couple relationship satisfaction (RAS, Hendrick, 1988) and depressive symptoms in the parents (BDI-I, Beck, Ward, Mendelson, Mock & Erbaugh, 1961) were included as control variables. Results: A significant effect of the triadic interaction on the child’s social-emotional difficulties was found. The effect explained 20% of the variance. However, this effect was not found in the psychomotor development. In addition, the mothers’ RF had a significant influence on the triadic interaction, explaining 21% of the variance. However, in contrast to the hypothesis, the mothers’ and fathers’ RFs were not significant variables as direct or indirect predictors to explain the child’s socio-emotional difficulties or psychomotor development. These findings show the importance of the RF on the quality of the mother-fatherchild interaction, which in turn influences the child’s social-emotional development. Additionally, the role of the father and the implications of these findings for research and clinical purposes are discussed.

El estudio tiene como objetivo explorar la mentalización de padres y madres hacia sus hijos que se encuentran en edad preescolar y que residen en Lima Metropolitana. Con este fin, se realizó un estudio de tipo cualitativo y diseño fenomenológico, aplicando la entrevista a profundidad a progenitores primerizos (cuatro parejas y una madre), cuyas edades se encontraban entre los 27 y 44 años. Los principales hallazgos indican que la mayoría de padres y madres muestran buena capacidad de mentalización; evidenciando sensibilidad para asignar razones acertadas al comportamiento emocional de sus hijos; y, consecuentemente, responder con conductas validantes y empáticas. Por el contrario, se encontraron, en algunos participantes, fallas en la mentalización ante momentos de tensión emocional; hecho que dio paso a conductas restrictivas e impulsivas con sus niños. Se resalta la importancia del vínculo cercano y el apego seguro entre progenitores e hijos para el desarrollo de la mentalización. Los hallazgos obtenidos pueden orientar el desarrollo de futuras investigaciones, respaldar la importancia de la mentalización y fundamentar la implementación de estrategias mentalizadoras en la crianza. / The study aimed to understand the mentalization of parents to children who are of preschool age and who reside in Metropolitan Lima. To this end, a qualitative study with a phenomenological design was carried out, applying the in-depth interview to first-time parents (four couples and one mother), whose ages were between 27 and 44 years. The main findings indicate that the majority of fathers and mothers show good mentalizing capacity; demonstrating sensitivity to assign correct reasons to the emotional behavior of their children; and, consequently, respond with validating and empathetic behaviors. On the contrary, in some participants, failures in the mentalization on moments of emotional tension were found; a fact that gave way to restrictive and impulsive behaviors with their children. The importance of the close bond and secure attachment between parents and children for the development of mentalization is highlighted. The findings obtained can guide the development of future research, support the importance of mentalization and the implementation of mentalizing strategies in parenting. / Tesis