What could be the reason for a four-month-old baby having little urine?

Possible reasons for reduced urine output in a four-month-old baby include insufficient fluid intake, excessive sweating due to hot weather, fluid loss from diarrhea, or incomplete development of kidney function. Parents should appropriately increase the baby's fluid intake and pay attention to the baby's eating and bowel movements. If symptoms persist or worsen, prompt medical consultation is recommended so that a doctor can make a diagnosis and provide appropriate treatment based on the specific condition.