Background: Childhood maltreatment is associated with early childhood developmental vulnerabilities. However, the extent to which higher levels of child protection responses confer benefit to developmental competencies, and the impact of earlier timing of first reports in relation to early childhood vulnerability remains unclear. Objective: We examined associations between early developmental vulnerabilities and (1) the highest level of child protection response (where OOHC was deemed the highest response among other types of reports/responses), and (2) the developmental timing of the first child protection report. Participants and Setting: Participants included 67,027 children from the New South Wales Child Development Study, of whom 10,944 were reported to child protection services up to age 5 years. Methods: A series of Multinomial Logistic Regressions were conducted to examine focal associations. Results: Children with substantiated maltreatment reports showed the strongest odds of vulnerability on three or more developmental domains (adjusted OR = 4.90; 95% CI = 4.13–5.80); children placed in OOHC showed slightly better physical, cognitive and communication competencies (adjusted ORs from 1.83 to 2.65) than those with substantiated reports that did not result in OOHC placements (adjusted OR from 2.77 to 3.67), when each group was compared to children with no child protection reports. Children with first maltreatment reports occurring in the first 18 months of life showed the strongest likelihood of developmental vulnerabilities on three or more developmental domains (adjusted OR = 3.56; 95% CI = 3.15–4.01) relative to children with no child protection reports. Conclusion: Earlier reports of maltreatment may signal the need for targeted remediation of early developmental competencies to mitigate early developmental difficulties.