Give at least 1 litre of water per day ..if no prior complaints like fever .just follow water intake.thats the remedy

Give the boy more of water Give Coconut water.  Shikanji Make it tastier so that he is encouraged to have more water

Less urine output is usually because of less water and fluid intake. Boys tend to sweat more than girls and so water is lost from the body like that. Try to increase fluid intake to 1.5 litres per day. It can be home made juices, lime juice, coconut water anything. Urinary tract infections can occur if water intake is less with features like fever, abdominal pain and vomiting