The first consideration is that the child’s urine is caused by physiological factors such as drinking too little water and sweating too much, and secondly, it may also be caused by ureteral stones, nephrotic syndrome, as well as other diseases such as renal failure. 1. Physiological factors: If the weather is hot, the child drinks too little water and sweats a lot, which may lead to a decrease in body fluids, then there will be less urine. 2. Ureteral stones: Ureteral stones may be caused by metabolic abnormalities, foreign bodies in the urinary tract, drug factors and other reasons. Patients will have hematuria, anuria, renal colic, oliguria and other manifestations, if the child has ureteral stones will have urinary oliguria. 3. Nephrotic syndrome: the cause of nephrotic syndrome is not clear, and it is considered to be related to genetic and immune function abnormalities. Patients will show a large amount of proteinuria, hypoproteinemia, decreased urine output and so on, so children with nephrotic syndrome will have symptoms of low urine output. 4. Other: the child’s urine is also considered to be due to renal failure, renal torsion, heart failure, hypotensive shock, severe water loss, blood loss and other causes. If it is a physiological factor that causes the child to urinate less, it will usually improve after drinking water. If it is a disease that causes the child to urinate less, then it is necessary to consult a doctor in time.