There is mixed international evidence about the impacts of long day care (LDC) on child development, with research suggesting benefits for some aspects of development but not others. Moreover, many of these studies have limitations including measuring a narrow range of developmental outcomes, utilizing parent reports of child development, and relying on small and/or non-representative samples. The aim of the current study was to explore the relationship between LDC and child development across five domains using teacher reported data from the 2021 Australian Early Development Census (AEDC). The sample were 166,467 children with available data on the key exposure (teacher-reported long day care attendance in the year before full-time school), confounders and child development outcomes. A series of Poisson regression analyses were conducted to explore the association between LDC and child development at school entry, after adjusting for child and family level confounders. Just over half of the sample (n = 92,611, 55.6%) attended long day care in the year before full-time school. In adjusted models, children who attended long day care had a lower relative risk (RR) of developmental vulnerability in fine and gross motor skills (RR=0.94, 95% CI 0.90-0.98), language and cognitive skills (RR = 0.79, 95% CI 0.76-0.82) and communication skills and general knowledge (RR = 0.81, 95% CI 0.78-0.84) than children who did not attend long day care. However, children who attended long day care had an increased risk of developmental vulnerability in social competence (RR = 1.23, 95% CI 1.19-1.28) and emotional maturity (RR = 1.38, 95% CI 1.33-1.43) than their peers who did not attend long day care. Findings highlight opportunities for the sector to grow supports for children's social and emotional development within LDC settings.