Purpos: The study aims to increase knowledge about early signs of relational difficulties in infancy and early childhood. We will look at how early such difficulties can be identified and examine factors that can predict relational difficulties. Furthermore, we aim to investigate the interaction and relational difficulties over time to understand what influences developmental pathways in adaptive or risky directions. Research Method: A sub-study of "Little in Norway: A study of children's development from pregnancy to 18 months." This is a prospective, longitudinal study where families are followed from pregnancy until the child is 18 months old, with repeated measurement points during pregnancy and after birth. About 1000 families from all over the country have been included in collaboration with selected health stations. In this sub-study, a particular focus is on video analyses of interaction recordings between mother–child/father–child. We have such recordings at three points when the children are 6, 12, and 18 months old. Analyses of the interaction recordings will be viewed with other data from the "Little in Norway" study, such as questionnaires from parents/childcare, test observations of the child, and information from pregnancy. After the video recordings are analyzed, statistical data analyses will be conducted, including regression analyses and structural modeling analyses. Results: Publications are planned, particularly focusing on the significance of depressive symptoms in mothers, both during pregnancy and postpartum. We will also examine how the duration and severity of such difficulties affect the interaction with the children. Furthermore, planned publications will illuminate the hypothesis of "differential susceptibility to environmental influence," which suggests that individual differences in children's temperament will cause them to be differently affected by their surroundings and care environment. Practical Significance and Research Implications: For the healthcare system, increased knowledge about relational difficulties in infancy and early childhood could provide a basis for developing early and targeted interventions to help families, infants, and toddlers at risk for developmental deviations. Research implications include greater knowledge of and understanding of possible multifactorial causal relationships between early risk factors, interaction difficulties, and children's later development and mental health.