Is a 21000 white blood cell count high for nine year old?

Yes, a white blood cell count of 21,000 is high for a nine year old. The normal range for white blood cell counts in children is 5,000-15,000 cells/µL. A high white blood cell count can indicate an infection or other medical condition. If your child has a white blood cell count of 21,000, it is important to see a doctor for evaluation.