Nearly one quarter of Australian children under the age of 5 experience multiple non-parental child care arrangements. Research focused on the relationship between multiple child care arrangements and child socioemotional development is limited, particularly in Australia. Evidence from the United States and Europe has linked multiple child care arrangements to increases in children's problem behaviors (de Schipper et al., 2004 and Morrissey, 2009), but there is little corresponding evidence on Australian children's child care experiences. Using a nationally representative sample of Australian children, we examined the associations between concurrent multiple child care arrangements and child socioemotional and behavioral development at age 4.5. We found suggestive evidence that child care multiplicity at age 4.5 is related to higher levels of behavior problems. However, this relationship is moderated by prior child care experiences. We found that prior care multiplicity mitigates the relationship between concurrent multiplicity and children's prosocial skills and conduct problems. In contrast, moving from a single arrangement or no non-parental child care to multiple arrangements appears to be negatively associated with children's concurrent socioemotional skills. Implications for policy and practice are discussed.