Isolated fracture of the sternum is an uncommon injury in a child. We report two cases of sternal fracture following falls from swings, which illustrate the mechanisms of injury in sternal fracture. One fracture resulted from a flexion compression injury of the thoracic spine, which has very rarely been reported in children. Sternal fracture should be considered in the differential diagnosis of acute chest pain in a child where there has been an activity involving hyperflexion force.