The study will aim to recruit all potential Crohn's disease children coming to a tertiary paediatric centre for colonoscopy. Once consented, an initial blood, urine and faecal sample will be requested along with 8 mucosal biopsies during the routine endoscopy session. If diagnosed with CD, and if the clinician prescribes treatment with EEN, an additional blood sample will be requested at the end of EEN, and 5 faecal and urine samples spread over 12 months; as well as some dietary information.