It is not unusual for children to suffer from diarrhoea. But if the lost salts and water are adequately replenished with oral rehydration solution (ORS), dehydration should not occur. You can give rice water, dal water or coconut water but I think giving ORS should be the best. In case of dehydration, the frequency of passage of urine comes down. So, if the child is passing urine adequately, you need not worry. If urinary frequency comes down, you can initially try giving more ORS but it is advisable to take the child to the emergency of a hospital with paediatric facilities.