A stomach ache or bellyache is called abdominal pain. If a child has abdominal pain that comes and goes regularly, they have recurrent abdominal pain (RAP).
Recurrent abdominal pain can be caused by a number of different illnesses or there may not be any underlying problem at all. If the child is seen by a doctor, and all medical causes are ruled out, then the child is said to have "functional abdominal pain". This means that there is no known cause for the pain.