Previous work identified a similar risk of injury for children seated on the struck side and center rear in side impact crashes in passenger cars. In order to further explain this finding, we investigated the effect of sharing the rear row with other occupants on injury risk and delineated differences in injury patterns among the seat positions. These analyses, conducted from a large child specific crash surveillance system, included: children 4-15 years old, rear seated, seat belt restrained, in a passenger car, and in a side impact crash. Injury risk was compared among each rear seat position stratified by the presence of other occupants on the rear row. Occupants are at an increased risk of injury if they sit alone on their row as compared to sitting with other occupants. Patterns of injuries distinct to each seat position were delineated.