Yes, urine output should be more. Baby needs oral fluids. Since baby has cough I would recommend warm milk, soups. Even warm water would do.
Some cough mixtures can lead to urine retention due to their side effects. Make sure the child doesn't take those.
Next Steps
baby should pass urine 4-6 times per day. report to hospital if baby doesn't pass urine for 6 hours straight even with adequate hydration.