Child restraint systems (CRSs) for vehicles are designed to provide protection and prevent or reduce child mortality and morbidity in road traffic accidents. Overall, 90% of children under 5 years of age in New Zealand currently use CRSs. There is considerable regional variability in CRS usage, but little information exists on its ethnic variations or determinants. “Increasing the level of restraint use” is explicitly stated as one of the 13 priorities within the New Zealand Ministry of Transport's new road safety strategy. As such, understanding CRS prevalence, patterns and associates within different communities is essential in realising this priority. Utilising a large birth cohort of Pacific children ( n = 1376 mothers), this study aimed to report the prevalence of maternal self-reported car seat usage at the 6 weeks, 1-year, and 2 years postpartum measurement waves; car/booster seat usage at the 4 years postpartum measurement wave; and to identify important associates using generalised estimating equation (GEE) models. Car seats were not used by 161 (11.8%) Pacific children at the 6 weeks measurement wave, 71 (5.8%) at 1-year, and 44 (3.8%) at 2 years, while car/booster seats were not used by 139 (13.3%) at the 4 years wave. Multivariable GEE model results revealed that mothers with no formal education, high parity, who smoked tobacco, lower household income, who lacked English language proficiency, and had multiple births were all at higher odds of failing to use car seat/booster seats. Despite differential attrition being noted in mothers over time, a sensitivity analysis using multiple imputation methods yielded similar findings. Targeted initiatives and education programs focusing on these higher risk groups, in particular, is needed to increase uptake and use of CRS thereby decreasing Pacific children's exposure to injury risk. As New Zealand has a large and increasing proportion of Pacific, Maori and Asian people, there is a continuing need to understand cultural factors in traffic safety. Only when culturally appropriate initiatives and education programs have been developed and disseminated that meet the needs of New Zealand's different communities is the national priority likely to be realised.