Post-traumatic cortical bone cyst is a rare occurrence in children. It is typically located in the distal radius, as a result of greenstick fracture. We report three cases referred to our fracture clinic as a tumour in bones. In one of our cases, the cystic lesion was noted following a displaced fracture in the femur, which is not previously published in the literature. The cyst-like lesion appeared as an oval radiolucency proximal to the previous fracture site on radiograph films. These lesions can cause concern for the on-call teams as they can mimic an infection or a tumour of the bone. We highlight the pathogenesis of the lesion with a review of the literature.