There is no need to start antibiotics like colistin in infants as a routine because most of the infections are viral and will not respond to antibiotics.
The only indication will be when there is fever
or there is blood in the stool when the doctor will decide to give antibiotics.
You give good amount of fluids and see whether child is passing urine well and not tired.The fluids are available in the form of sachets of ORS
with all instructions as to how to use.