Children with overactive bladders have a need to urinate more often than usual because their bladder muscles have uncontrollable spasms. The muscles surrounding the urethra -- the tube from the bladder that urine passes through -- can be affected. These muscles are meant to prevent urine from leaving the body, but they may be "overridden" if the bladder undergoes a strong contraction.
Urinary tract infections can cause a need to urinate as the urinary tract becomes inflamed and uncomfortable. Certain neurological conditions may cause these symptoms.
Another cause of overactive bladder is a condition called pollakiuria, or frequent daytime urination syndrome. Children who have pollakiuria urinate frequently. In some cases, they may urinate every five to 10 minutes or urinate between 10 and 30 times a day. This condition is most common among children aged 3 to 8 and is present only during waking hours. There are no other symptoms present. Doctors believe that pollakiuria is related to stress. Usually, the condition goes away after two to three weeks without requiring treatment.