Objectives Parental supervision reduces young children's risk of unintentional injuries, but supervision by older siblings has been shown to increase risk. The current study explored how this differential risk of injury may arise.

Methods The supervision behaviours of mothers were compared to those of their older children when each was the designated supervisor of a young child in their family in a setting having ‘contrived hazards’.

Results Mothers engaged in more proactive safety behaviours by removing hazards, whereas older siblings more often modelled injury-risk behaviours by interacting with hazards, and supervisees were likely to interact with hazards the older sibling touched. Supervisees displayed more injury-risk behaviours when supervised by a sibling, yet sibling supervisors were less attentive to supervisee risk behaviours than mothers. Supervisees also were more non-compliant with older siblings than mothers when requested to stop risk taking.

Conclusions Both supervisor and supervisee behaviour patterns contribute to increase the risk of injury when older siblings supervise younger ones.