The potential of early years' childcare to reduce mental health inequalities of school age children in Scotland.

Preschool childcare is considered an important policy for reducing inequalities in children's cognitive and socio-emotional development, although the population-level benefits for children under three years, is less clear. We examined the potential for childcare across the whole early years' period to benefit mental health and reduce inequalities, under different hypothetical policy scenarios, in the Growing Up in Scotland study. Marginal structural logistic regression models estimated odds ratios (ORs) to quantify inequalities in mental health and consider how these would be altered under different hypothetical scenarios. Mental health (the outcome) was measured using the total Strengths and Difficulties Questionnaire score at the start of primary school. Socioeconomic circumstances (the exposure) were represented by maternal educational measured in infancy. Sequence analysis identified common patterns of childcare usage from 10 months to four years (the mediator). Confounders were adjusted for using inverse probability of treatment weights and analyses accounted for sampling design and attrition (complete case sample,