This paper uses data from a major Australian longitudinal study to test the extent to which children recruited on the basis of attending an early childhood education and care (ECEC) setting when they were 3–4 years of age received an ‘optimal’ dosage of education and care. The idea of an optimal dosage is drawn from research literature on what level of dosage leads to improved learning and development outcomes for children. This dosage level is then compared with the actual level received by Australian children, through examining the age of entry of Australian children into ECEC and the number of hours of education and care they receive before school entry. Key predictors of the total hours of ECEC usage and the year of commencement in formal ECEC programs are reported, and demonstrate the variability and correlates of participation in ECEC programs. Patterns of ECEC usage were predicted by family advantage and disadvantage factors. Children from homes with less employment, and more siblings, tend to use fewer hours of ECEC before school and/or start later. The findings suggest sub-optimal levels of participation given the policy goal of improving learning and developmental outcomes for all children and particularly for children from disadvantaged backgrounds. Policy implications are addressed.