Early mental health inequalities among preschool children in Portugal: a cross-sectional study of social, family and health behaviour correlates

Background Mental health difficulties in early childhood may affect development and contribute to later inequalities, yet community-based evidence remains limited in Portugal. This study estimated the proportion of preschool children with mental health difficulties and examined associations with immigrant background, socioeconomic and family circumstances, perinatal factors and health behaviours. We also compared children with and without an immigrant background. Methods We conducted a cross-sectional analysis of baseline data from children recruited through primary health care centres in the Lisbon Metropolitan Area between May 2022 and December 2024. Of 760 participants, 453 children aged ≥ 4 years with a valid parent-reported Strengths and Difficulties Questionnaire (SDQ) Total Difficulties score were included. Caregivers reported sociodemographic, family and perinatal characteristics and health behaviours. Early mental health difficulties were defined as borderline/abnormal Total Difficulties scores (≥ 14). Immigrant background was defined by the child or at least one parent being born outside the European Union. Multivariable logistic regression examined associations in 417 children with complete data; an additional negative binomial model analysed the undichotomised SDQ Total Difficulties score. Results Among the 453 children, 23.6% scored in the borderline/abnormal range. Higher adjusted odds were observed for household incomes of >€750–€1,500 versus >€1,500 per month (aOR = 2.10, 95% CI: 1.13–3.90), extended or other family arrangements versus nuclear households (aOR = 1.82, 95% CI: 1.02–3.26), and no sports participation (aOR = 2.80, 95% CI: 1.59–4.94). Children with an immigrant background showed greater socioeconomic disadvantage, higher screen exposure, lower sports participation and more often scored in the abnormal range for peer relationship problems (12.5% vs. 5.7%). The association with immigrant background was attenuated after adjustment, with no clear independent association remaining (aOR = 1.09, 95% CI: 0.66–1.79). The full-score analysis supported the association with no sports participation; estimates for income and family structure were less conclusive. Conclusions The findings highlight the importance of considering children’s economic and family circumstances and daily routines in early identification and intervention. Primary care and community services may help families access appropriate support. Longitudinal and intervention studies are needed to clarify these relationships and assess potential preventive effects.