Most probably your son has an attack of acute gastroenteritis (an infection of the gastrointestinal tract), commonly due to viral infection. The episode usually subsides on its own with rehydration and continued feeding. During the acute attack, ORS is given generally to replenish the water and electrolytes lost in diarrhoea and vomiting. It is not a replacement for the food. Continue to feed the child during acute diarrhoea.
Breast feeding should be continued uninterrupted even during rehydration with ORS. Staple foods enriched with fats and oils to provide calories (e.g., khichri with oil, rice with milk or curd and sugar, mashed banana with milk or curd, mashed potatoes with oil and lentils) are preferred. Foods with high fibre content (coarse fruits and vegetables) should be avoided. In a non-breast fed child, cow or buffalo milk can be given undiluted after correction of dehydration together with semisolid foods. Milk should not be diluted.