Inflammatory bowel diseases (IBDs), including Crohn disease (CD) and ulcerative colitis (UC), often affect children and adolescents. Their diagnosis is based on the integration of clinical, biological, endoscopic, histological and radiological data. The paediatric radiologist may help the clinician in many ways. In children presenting with symptoms compatible with IBD, gut exploration by US may identify those who will benefit from more invasive explorations including endoscopy. During the process of diagnosis, small bowel exploration has a crucial role in differentiating CD from UC and in classifying the disease into subphenotypes. Finally, new imaging methods are useful during patient follow-up for assessing disease activity and for the diagnosis of complications.