D.S.
You may want to consider having your child examined by a chiropractor.... sometimes the position of the tailbone can have an affect on the nerves that affect bladder control. It may just be a simple adjustment that will help him... hence why it may only happen time to time depending on the position he may be sleeping in due to the pressure on the spine. I am a Chiropractor and I have been able to help several little ones end their bed wetting by adjuting their lower back..... I would be happy to answer any qiestions you may have.