your son probably has gastroenteritis, which is an infection , usually viral , in this intestines , that causes fever , vomiting and loose motions. the concern here if does not get enough fluids he might get dehydrated , so providing him with appropriate amount of fluids in the form of water , milk , soup , will prevent it , even if vomits a little , the majority his body will absorp . now , a few things that if you notice , then go visit his doctor : if there is significant abdominal pain , irritability , your son doesn t seem well and active when the fever goes away , if the fever persists and finally if he is intolerable to any oral feeds I hope this helps