The common causes of hematuria in a 6-year-old child with red blood cells in the urine include acute glomerulonephritis and urinary tract infection. 1. Acute glomerulonephritis: often with acute onset, clinical manifestations include hematuria, accompanied by edema, hypertension and proteinuria, and may have renal insufficiency. 2. Urinary tract infection: including pyelonephritis, cystitis and urethritis. Clinical manifestations of bladder irritation, may have back pain, fever and chills, etc., visible hematuria. If the red blood cells in the urine <2/high-power field of view, it is a normal phenomenon, no need to be nervous; if the red blood cells in the urine >3/high-power field of view, suggesting hematuria, you should go to the hospital in a timely manner, to clarify the causes of hematuria, and under the guidance of the doctor for treatment.