My 6yo actually has had (and still has) a problem with day-wetting (rarely night), with frequent SPRINTS to the bathroom, often too late. There were no other symptoms, but the doctor noted and tested for a UTI - came back positive. I stress that there were no other symptoms, because we usually look for child complaining about pain during urination, and it wasn't there.
Have the doctor do a urine culture to be sure - the longer it's left untreated, the worse it becomes, traveling up and damaging the bladder and kidneys.
BTW: recent press about an herbal supplement that's been shown to help prevent recurrence of UTIs, when used in conjunction with antibiotics, called "Forskolin". Not sure how good, but the press release out of Duke University earlier this week looked good.