Thank you for your query,
As your grandson is having intermittent episodes of upset stomach, low grade fever
evaluate him with basic investigation like CBP, CUE, ultrasoung abdomen and pelvis to look for any urine infections or any underlying problems.
Stool examination to be done to look for any ova, cysts to look for parasites.
Consult your Pediatrician
once for exmination and evaluation.
Hope I have answered your query.