Background Parenting programmes aim to support parents’ skills and confidence, improving parenting and, in turn, children’s mental health. Thus they have the potential to reduce population prevalence (and inequalities) in child mental health problems. We modelled the potential population impact of scale-up of parenting interventions in a national cohort. Based on review evidence, we simulated interventions with effect sizes of 0.9SD (intensive) and 0.4SD (standard).

Methods We used data from the UK Millennium Cohort Study, following 18 000 children born 2000–2002. Parenting was assessed by Child-Parent Relationship Scale (CPRS: Short-Form) score when the child was 3 years. Child mental health problems (CMHP) at 5 years were assessed by Strengths and Difficulties Questionnaire (SDQ) total score, dichotomised using an established cut-off. Socio-economic circumstances were represented by mother’s highest academic qualifications (<GCSEs A-C; GCSEs A-C and above) at 9 months.

Predicted probabilities of CMHP were estimated, fitting marginal structural models to examine the mediating effect of parenting, accounting for confounding using inverse-probability-treatment-weights. Inequalities were assessed with Risk Ratios (RR [95% CIs]). A series of intervention scenarios were simulated by re-estimating predicted probabilities after modifying the CPRS score (to reflect effectiveness) for eligible children (targeting).

We analysed data from 14 540 children, using Stata 13.1. Survey weights and multiple imputation addressed missing data.

Results Overall prevalence of CMHP at 5 years was 10.8%, and children of mothers with low educational attainment had a greater risk of CMHP (RR=2.46 [95%CI:2.24–2.70]). Focusing on three parenting intervention scenarios, we showed changes in CMHP prevalence and inequalities compared to those observed: 1. Universal (standard support to all parents): prevalence change −2.5%; inequality RR=2.56[2.30–2.85]; 2. Targeted (intensive support to families receiving means-tested benefits): prevalence change −1.4%; inequality RR=2.11[1.91–2.34]; 3. Progressive universal (intensive support for families receiving benefits and standard support for others): prevalence change −3.2%; inequality RR=2.35[2.10–2.62].

Conclusion Large inequalities in CMHP were apparent by age 5 years. In simulated scenarios, inequality was reduced through an intervention that explicitly set out to provide intensive support to disadvantaged families. In contrast, reductions in overall prevalence were more likely to be achieved by universal interventions. A progressive universal approach (combining intensive support for disadvantaged families with standard support for others) led to a reduction in both population prevalence and inequality. Nevertheless, in all intervention scenarios, inequalities in CMHP remained strong. These results suggest that parenting interventions may contribute to a reduction in CMHP inequalities, particularly when including targeted support for disadvantaged families.