I commend any parent who does not get mad at their child for this! I believe that it can be something as simple as bad dreams, anxieties and such. But first I would recommend taking him to the doctor to rule out any type of bladder or urinary tract infection.
Our daughter started wetting the bed at age 7. Because I have three other children the same age this was embarrasing for her. So we bought her pull ups (cheapest I've found are at a Wallgreens store) and a diaper pail. We put everything in the bottom dresser drawer and allowed her to privately get ready for bed and two years later our other three still have no clue that our daughter wears pull ups to bed.
Since then we have found that with our child it is because of a medical problem called Lichen Sclerosis (sp?). This is very rare but I would strongly recommend having a doctor rule out anything. And after that just be kind. I even went so far as to tell my daughter that I wet the bed until I was almost 12 years old. It was our secret and it seemed to calm her embarrasement.
Good luck!!