Heterotopic ossification (HO) is the growth of bone in soft tissue, and can be broadly classified into neurogenic, genetic and traumatic causes. The pathophysiology of HO remains unknown. This disorder is extremely rare in infants and can mimic or coexist with thrombophlebitis, cellulitis or osteomyelitis. Most importantly, HO has to be differentiated from bone-forming tumours such as osteosarcoma and osteochondroma. We report a case of traumatic HO in a fiveday- old newborn following intravenous cannulation of the right wrist and left ankle, with the latter complicated with osteomyelitis. We highlight the clinical and radiological features of HO and differential diagnoses of soft tissue ossification in early childhood.