Background The benefits of correctly using size-appropriate restraints for children travelling in cars are well established, and considerable research has focused on the determinants of appropriate restraint choice. There are few studies of the factors associated with incorrect use.

Objective To determine predictors of incorrect restraint use by child occupants and how these differ from inappropriate use.

Methods A stratified multistage cluster sample of child occupants aged 0–10 years in New South Wales, Australia was used. Observation of restraint type and inspection of correctness of use was performed on arrival at schools, childcare centres, and child health clinics. An interview was conducted with the driver. Logistic regression was performed to estimate the effects of parental, family, and other characteristics on the likelihood of moderate or serious incorrect restraint use for restraint classes (rear/forward facing, booster, and seatbelt).

Results Significant factors varied depending on age and restraint class. Older child restraint users (OR per year of age 0.27, 95% CI 0.07 to 0.98) and seatbelt users (OR per year of age 0.54, 95% CI 0.45 to 0.64) were less likely to be incorrectly using their restraints than younger users. Child restraint and booster users from non-English speaking families were more likely to be incorrectly using their restraints. Having more children in the car appeared to reduce incorrect use for booster (OR 0.18, 95% CI 0.06 to 0.57) and seatbelt users (OR 0.39, 95% CI 0.16 to 0.93).

Conclusions There is a need to reduce incorrect restraint use by both education and improved restraint design. Education aimed at reducing incorrect use may need to be targeted differently to appropriate use programmes, as the predictive factors differ.