The Longitudinal Study of Australian Children is a major study on child development, following two cohorts of 5,000 children each: infants aged 3-9 months at the beginning of the study and preschool children aged 4-5 years. A previous article described the development of outcome indices for the study, which feature 16 measures over three domains: health and physical development, social and emotional functioning, and learning competency. This article presents evidence from Wave 1 of the study to support the validity of the indices.