ObjectiveThe current study aimed to quantify the real-world, everyday travel behaviours of child vehicle occupants and associations with child restraint systems (CRS)/booster seat (BS) head positions that are suboptimal in terms of crash injury risk. MethodsThe data from a naturalistic driving study (NDS) provided 414 trips for analysis. Child occupant behaviour, head position within their forward-facing CRS (FFCRS) or BS and other relevant information was coded for nine discrete 5 s intervals or ‘epochs’ (5%, 17%, 25%, 30%, 50%, 53%, 75%, 89% & 95% of trip duration). A total of 2158 epochs were analysed. The relative contributions of factors of interest to suboptimal head position were explored through a generalised estimating equation (GEE), which accommodated correlation between measurement in each epoch for an individual child. ResultsThe GEE revealed that, when compared to child occupants travelling in a FFCRS, child occupants travelling in a BS were twice as likely to have a suboptimal head position. Child occupants were also nearly one and a half times more likely to have a suboptimal head position if they were in the older age range for the restraint type that they were using (FFCRS or BS), if they had incorrect shoulder belt/harness use, or if they were interacting with other vehicle occupants. In addition, when compared to engagement in conversation, children's engagement in a lap-based activity (including use of electronic devices, toys and reading) increased the odds of suboptimal head position by nearly two and half times,. ConclusionsThis study identified key factors associated with child occupants’ head positions when travelling in a CRS. These findings suggest that various head positions are adopted during everyday travel. Future restraint and vehicle designs that improve the ability of child occupant protection systems (CRS and vehicle-based devices) to safely accommodate a wide range of suboptimal head positions that were commonly observed during everyday travel are encouraged.