Objective Assess the association between caregiver supervision and acute unintentional injury in young children; evaluate whether lower levels of supervision result in more severe injury.

Methods A case cross-over study was conducted. Parents of children aged ≤4 years whose injuries required emergency department (ED sample) treatment or admission to the hospital (inpatient sample) were interviewed. Information on supervision (3 dimensions: proximity, attention, continuity) at the time of injury and 1 h before the injury (control time) was collected. An overall supervision score was created; a higher score indicates closer supervision. Hospital admission served as a proxy for injury severity. ORs and 95% CIs were calculated.

Results Interviews were completed by 222 participants; 50 (23%) were in the inpatient sample. For each supervision dimension the inpatient sample had higher odds of injury, indicating effect modification requiring separate analyses for inpatient and ED samples. For both samples, proximity ‘beyond reach’ was associated with the highest odds of injury; compared with 1 h before injury, children were more likely to be beyond reach of their caregiver at the time of injury (inpatient sample: OR 11.5, 95% CI 2.7 to 48.8; ED sample: OR 2.9, 95% CI 1.8 to 4.9). Children with lower supervision scores had the greatest odds of injury (inpatient sample: OR 8.0, 95% CI 2.4 to 26.6; ED sample: OR 3.3, 95% CI 1.9 to 5.6).

Conclusions Lower levels of adult supervision are associated with higher odds of more severe injury in young children. Proximity is the most important supervision dimension for reducing injury risk.