I would definitely talk to his pediatrician. There could be physiological reasons as well as psychological reasons why this is happening. I think it is best to know the reasons as soon as possible, so you can resolve it as soon as possible.
Do nothing, it will stop when his body is ready, theres nothing wrong with bed wetting and you tell him that its normal. With some people it takes longer, i know someone who was bed wetting till they were 14.
B4 looking into any treatment its best to see his GP first and talk to him about it if your really concerned.