Mesenteric lymph node enlargement is an imaging description and not a diagnosis of disease per se. The cause can be the normal development of the intestinal immune system in response to events or the intestinal environment, or it can be a viral infection resulting in mesenteric adenitis. It is important to exclude other acute abdominal conditions such as intussusception, appendicitis, and some rare infections (TB, Yersinia). The most common is due to a viral infection. The symptoms are abdominal pain, sometimes accompanied by symptoms of gastroenteritis, i.e. diarrhea and vomiting. Drink as much water as possible to avoid dehydration if you are still able to drink. If you vomit even after drinking water, you may need intravenous fluids. Most children will heal on their own within a few days. Sometimes pain medication is needed, and when you start eating again, start with easily digestible foods, such as porridge or crackers. For viral infections the normal human immune system produces antibodies that fight off the virus. Sick children with low immunity sometimes need anti-viral medication. Their side effects are great and more than one can be damaging to the liver.