for anyone stumbling on to this thread with an older kid that's still night wetting...this can be a symptom of disordered sleep.
Have their tonsils and adenoids checked! If breathing is disrupted even slightly the body will override wake signals to prioritize sleep over peeing.
I have 4 kids and have cared for dozens more through the years. Like with anything, your mileage may vary. Some kids need zero help and do it on their own, some kids need typical intervention and help, and some kids have issues well into their pre-teen years (or older!).