"Diarrhea caused by a viral infection usually lasts several days to 2 weeks, regardless of the type of treatment. The main goal of treatment is to prevent dehydration. Your child needs to drink enough fluids to replace the fluids lost in the diarrhea. Don't expect a quick return to solid stools."
https://www.summitmedicalgroup.com/library/pediatric_health/hhg_diarrhea_formula/