Does hypnotherapy work on children with bed wetting?

Sometimes. Better to try simple measures first, ie restricting fluids, lifting to toilet at night, bedwetting alarm or medication.
Yes. Actually, I do not have experience with this in children but was very successful in treating an adult patient with bed wetting. Once again, the hypnosis is a tool and one has to decide how to approach the problem using that tool. The fact that one has not done a scientific study, does not necessarily mean that the treatment does not work.
Absolutely. I've worked with many children suffering from difficulty with dry beds by using hypnosis. The child can typically achieve dryness after only a few sessions unless there is some underlying medical problem or a pyschologic need to have a wet bed.
No convincing data. Bladder alarm has been the most effective treatment for night time bed wetting.