Usually never. Isolated bedwetting is rarely "abnormal" but it can be very socially stigmatizing. Bedwetting occurs in normal people at rates of 15% of 5 y/o, 5% of 10 y/o, and 1% of 18 y/o. It is considered abnormal if it recurs after a prolonged absence (no wetting for more than 6 months) or if it associated with any other neurologic problem, urinary infections, pain, daytime incontinence, etc.
What parents think. Is abnormal. Depends upon parents own nexperience as chidren. Some parents and doctors think bedwetting once or twice a week in a seven year old is abnormal others don't. Certainly bedwetting 3 or 4 nights a week in a ten year old is abnormal. 15% of 5-year-olds wet their beds regularly, thus I consider that normal, but worth restricting fluids after supper and toileting them late if, if it works.