Background and objectives Crash injury risk is reduced when a child correctly uses an appropriate restraint; however, incorrect restraint use remains widespread. The aim of this study was to determine whether product information developed using a user-driven approach increases correct child restraint use.

Methods We conducted a two-arm double-blinded parallel randomised controlled trial in New South Wales, Australia 2019–2021. Participants were current drivers who were either an expectant parent or a parent of at least one child residing in the greater Sydney metropolitan area who were interested in purchasing a new child restraint. The intervention was user-driven product information consisting of instructions printed on an A3 sheet of paper, swing tags with key reminders and a video accessed via Quick Response codes printed on the materials. The control group received a postcard summarising legal child restraint requirements. The primary outcome was the correctness of child restraint use observed during home visit approximately 6 months after restraint purchase. Correct use was defined as no serious error or <2 minor errors. The secondary outcome was a count of observed errors.

Results 427 participants were recruited. Home visits were conducted for 372 (190 intervention and 182 control). Correct use was more common in the intervention group (37.4%) compared with the control group (24.2%, p=0.006). Participants receiving the intervention were 1.87 times more likely to correctly use their restraint than those in the control group (95% CI 1.19 to 2.93).

Conclusions The results provide evidence for the effectiveness of user-driven instructions as a countermeasure to restraint misuse.

Trial registration number ACTRN12617001252303.