My research investigates the associations between family financial hardship and offspring’s mental health and criminal behaviours across childhood, adolescence, and adulthood using the ALSPAC longitudinal datasets. The research aims to identify mediating factors of the associations and explore how shifting financial circumstances impacts mental health through counterfactual analysis. I use advanced quantitative methods, including Growth Curve Modelling and Structural Equation Modelling, to examine developmental trajectories and relationships over time. The findings will inform interventions and policies to address youth mental health, criminal behaviour, and social inequality.