Two children aged 3 months and 14 years developed heparin‐induced thrombocytopenia whilst receiving heparin. The clinical course was complicated by renal vein thrombosis in the 3‐month‐old infant and subcutaneous haemorrhage requiring resuscitation in the 14‐year‐old child. Anticoagulant therapy was discontinued immediately in the 3‐month‐old child. In the 14‐year‐old child, because of the need for continued anticoagulation therapy, low molecular weight heparin was used until warfarin cou