Objectives This study examined the risk factors for non-participation in a developmental surveillance program in a population in south-west Sydney with a high proportion of culturally diverse and socioeconomically disadvantaged people. Methods Data from 850 and 625 12- and 18-month-old children respectively from the Watch Me Grow (WMG) birth cohort were used for this study. Logistic regression models were used to assess risk factors for 12- and 18-month non-attendance at Well Child Visits, as well as non-completion of the developmental surveillance questionnaire Parents' Evaluation of Developmental Status (PEDS) in the child's personal health record (PHR). Results Independent risk factors for non-attendance at Well Child Visits were female sex of the child (odds ratio (OR) 12 months 1.5; 95% confidence interval (CI) 1.0-2.3), mother's country of birth Australia (OR 18 months 1.8; 95% CI 1.2-2.7), annual household income less than A$25001 (OR 12 months 1.8; 95% CI 1.0-3.2) and residing in a socioeconomically disadvantaged neighbourhood (OR 12 months 1.7; 95% CI 1.1-2.5). Independent risk factors for non-completion of PEDS in those who did not attend the Well Child Visit compared with those who did attend and did complete PEDS were household annual income at birth less than A$25001 (OR 12 months 3.9; 95% CI 1.9-8.1) and residing in a socioeconomically disadvantaged neighbourhood (OR 12 months 2.1 (95% CI 1.2-3.7) and OR 18 months 2.0 (95% CI 1.2-3.6)). Conclusions In this population, children exposed to socioeconomic disadvantage are less likely to have attended a Well Child Visit and to have a completed PEDS in their PHR at 12 and/or 18 months of age. What is known about the topic? Developmental problems are common in early childhood, and children from socioeconomically disadvantaged households are at higher risk. Universal developmental surveillance programs may be effective at early identification of children at risk of developmental problems. Early childhood interventions, when accessed, can lessen the effects of developmental problems in later years. What does this paper add? This paper highlights that children exposed to socioeconomic disadvantage in early childhood who are at higher risk of having developmental problems are also at higher risk of missing out on early identification by non-participation in universal developmental surveillance. What are the implications for practitioners? A more equitable model of developmental surveillance should include a framework of proportionate universalism to ensure optimal engagement of high-risk population groups.