To examine socio-demographic factors associated with maternal help-seeking for child developmental concerns in a longitudinal birth cohort study. An understanding of these factors is critical to improving uptake of services to maximise early identification and intervention for developmental concerns.A birth cohort was recruited from the post-natal wards of two teaching hospitals and through community nurses in South Western Sydney, Australia, between November 2011 and April 2013. Of the 4047 mothers approached, 2025 consented to participate (response rate = 50%). Socio-demographic and service use information was collected after the child's birth and when the child was 18 months of age. Sources of help were divided into three categories (formal health services, other formal services and informal supports) and compound variables were created by summing the number of different sources identified by mothers.Significantly more sources of help were intended to be used and/or actually accessed by mothers born in Australia, whose primary language was English, with higher levels of education and annual household income, and among mothers of first-born children.Developmental concerns are known to increase with increased psychosocial adversity. Our findings of reduced intent to access and use of services by socio-economically disadvantaged families and those from culturally and linguistically diverse backgrounds suggests that an inverse care effect is in operation whereby those children with the greatest health needs may have the least access to services. Possible explanations for this, and recommendations for improving service accessibility for these populations through targeted and culturally appropriate services, are discussed.