I am sorry to hear about pur son. I was diagnosed at 14 and unfortunately I remember it all too well. To address your question, the intestines, which are essentially hollow tubes, are lined with cells that help us absorb the food we eat. To protect us bugs we may consume with food, the intestines also have a lot of immune cells. In Crohns disease, these cells become over active and cause inflammation. The inflammation results in damage to the cells that line the intestine which causes holes and pits in the intestines which are known as ulcerations. Ulcerations allow bugs in the intestines, the majority of which are normal residents, enhnaced contact with immune cells and the inflammation gets enhanced. One of the agents that causes inflammation is cytokine called TNF which is blocked by both Remicade and Humira. I have been on Remicade and did very well on it for a number of years. Remicade is admistered IV according to a schedule set by your doctor at an outpatient facility. Overall, not a major inconvenience. Humira is given by injection and can be done at home in few minutes once your doctor shows you how. Given that your son is young and missing school can be frustrating, humira may be more convenient. You should discuss that with your doctor.
I hope your son starts to feel better. All the best.