hello, welcome to hcm thanks for the query Diarrhea results in large losses of water and electrolytes.so give your baby enough oral rehydrating solution.if your baby is mildly dehydrated then it can be treated at home using 100 mL of ORS/kg/24 hr until the diarrhea stops.initially give in small amounts in short intervals.if dehydration is severe then hospital admission is needed.50 mL/kg of the oral rehydration solution (ORS) should be given within 4 hr to patients with mild dehydration and 100 mL/kg over 4 hr to those with moderate dehydration. give additional 10 mL/kg of ORS for each stool. if your baby is having dysentry then he/she may need antibiotic syrup.also econorm sachet is helpful in this condition rash is more common in this conditions because of frequent wetting of buttock groove. .follow the simple measures- 1-change the diaper frequently 2-keep the area dry 3-clean that are with gentle cleansing and the apply ointments containing petrolatum or zinc oxide after it 4-also rule out the possibility of fungal infection. if after all the measures its not coming down then you can apply 0.5 % hydrocortisone ointment to that area under the consultation of pediatrician take care