Hi welcome to HCM.... Your son having loose motion for which doctor suspecting colitis especially anaerobic infection or by amebic colitis ..... So given metronidazole tablet ... In diarrhea normal bacterial flora can be lost ...So usually we are prescribing taking probiotic tablet to replenish flora.... Yes sporlac also can be taken.... Dose is two times daily in morning and evening..... Here maintain hydration with lots of fluid.... Fruits taken more ..... Hot water given for drinking for few days.... If still no benefit USG abdomen and stool microscopic examination done for further work up.... Hope your concern solved... Take care