Social inequality is the unequal distribution of socio-economic (SES) resources which affects people’s standards of living. Typically, individuals from lower SES backgrounds have a higher risk of poor physical and mental health, and children, have an increased likelihood of developing emotional and behavioural difficulties. Multiple factors such as family stress or genetics can influence this relationship between SES position and mental health difficulties. For example, low family income can contribute to difficulty in affording needs and parental distress, which in turn may lead to harsher parenting or family conflict which affect child development. Some of the exposures associated with low SES position can lead to heritable changes in gene expression without altering the DNA sequence which could then affect mental health outcomes. These changes are known as epigenetics, and DNA methylation (DNAm) is the most common epigenetic mechanism through which social inequality can affect gene expression. Low SES position has been previously associated with more alterations to DNAm profiles compared to higher SES positions. DNA methylation occurring in some gene regions have also been observed to associate with child mental health difficulties. Therefore, in this study we propose to investigate the relationship between SES position and child mental health difficulties, and whether this relationship can be explained by epigenetic changes and family functioning. We will make use of multiple methods, most notably structural equation modelling (SEM) for longitudinal analysis of participant data from the Avon Longitudinal Study of Parents and Children (ALSPAC).