Background In March 2010, new child restraint legislation was implemented in NSW, Australia which required child passengers up to the age of seven travelling in a motor vehicle to be restrained in an age-appropriate restraint. There is conflicting evidence for the impact of changes in legislation. Studies that fail to find reductions in injury may be limited due to short periods of follow-up, the types of datasets used, and use of methods that assume an abrupt, specified change time-point directly aligned with date of the law change.

Objective To examine injury rates in child passengers before and after implementation of new child restraint legislation in NSW, Australia in March 2010, with a legislation time-period and a control group.

Methods An interrupted time series (ITS) approach in SAS was used to investigate the trends in hospital admitted injury among children aged 0–14. The data used for this analysis was collected through linked administrative datasets between 1 July 2001 and 31 March 2019. Monthly injury admission number and rate were aggregated and adjusted to the population. The temporal data was split into three time periods: pre-legislation (July 2001 – October 2007), legislation (November 2007 – December 2011), and post-legislation (January 2012 – March 2019).

Results Across the study period, there were 2940 injury cases. For each age group, 213 data-points/months over the study period were analysed. When comparing children aged 11–14 years and pre-legislation period, the injury rate for age-group zero, those 1–6 years, and 7–13 years reduced by 49% (IRR= 0.51, 95% CI= 0.12–2.12), 36% (IRR= 0.64, 95% CI= 0.30–1.37), and 37% (IRR= 0.63, 95% CI= 0.27–1.47), respectively, in the post-legislation period.

Conclusions The lack of detailed information on the use of child restraints in each injury case, coupled with the small sample size of severe injury cases, may limit the conclusiveness of our findings. Future research analysing media and market reports could offer a more comprehensive understanding of the impact of legislation on child restraint usage at the population level.