I would think that one of the more common causes would be a urinary tract infection. This can occur in young girls when not wiping from front to back after using the toilet. It will cause frequent urination. Your doctor should be able to confirm this with a urine sample.
An overactive or anxious child frequently urinates. Also it is possible large amount of fluid intake may cause frequent urination. Another scenerio is that the childs bladder is actually growing more rapidly that other parts of the body. If problem continues, try to increase fiber intake and consult a doctor.
Urinary Tract Infection, Stone in kidney, ureter or bladder , Juvenile diabetes, abnormal psychology [if she is wetting bed], traumatic injury to urinary tract, renal tuberculosis or some drugs.
Frequent urination can be the sign of many different problems. Frequent urination can be associated with high blood sugar which may be diabetes. A urinary tract infection is a possibility.
