Symptoms come and go over days, weeks, or months. Children with a low fever can seem to be fine. When it flares up, the child will look and act sick. Children can have good days with few or no symptoms, and worse days with flare-up symptoms. This condition may also cause inflammation of the lining of the lung, called pleuritis, or the lining of the heart, called pericarditis. It can cause swollen lymph nodes, and an enlarged spleen and liver. Children who have it may grow more slowly than normal.