This two-phase study is being conducted to determine the reasons why some children with newly diagnosed Crohn's disease heal their bowel inflammation after one type of therapy and why others do not. To do this, the study team will ask to collect blood, stool and biopsy (tissue) samples from participants newly diagnosed with Crohn's disease to measure their inflammation markers and evaluate their genes (DNA). To determine how much a participant's bowels have healed, we will also compare colonoscopy and MRE results that occur as part of the participant's standard clinical care.