So do about 7% of his mates according to a great patient support website on this topic (termed enuresis in medical jargon) called www.eric.org.uk. And, if you ask his grandparents, you may find that there is a seldom spoken about family history of it as well.
The important thing that the doctor or nurse seeing your child has to ascertain is “has he ever been dry at night?” Children who have been dry for over 6 months and have started wetting again need to be checked for a urine infection, diabetes or emotional upset. The vast majority of 8 year old children who wet the bed have never been dry and end up with a diagnosis of primary nocturnal enuresis which is something that they should grow out of but may need help with especially if it is starting to affect their social lives, sleepovers, cub camps etc.
The problem is caused by 1 or more of: an inability to wake up to feelings of fullness in his bladder, an overactive bladder or a delayed maturation of the gland in his brain which secretes a hormone which stops most of us producing as much urine at night. Your GP, paediatrician or school nurse should be able to work out from your son’s history which aspect is affecting him most and, taking into account his age, can then decide on the appropriate way forward.
Enuresis services are quite stretched (because it is such a common problem) and tend to only see children from the age of 7 although they are supposed to now offer appropriate information to parents of younger children too if it is affecting family harmony. Some studies suggest that if a child is still wetting when older than 11, it starts to get harder to sort it out for them so I wouldn’t leave it too late to get him initially assessed.
All the background information, explanations and advice you and your child need is at http://www.eric.org.uk/Bedwetting/info_bedwetting_wetting_parents. They also have an on-line shop for such things as alarms, disposable and washable protective bedding covers etc. Another resource is the parent information leaflet from the recent NICE guideline on enuresis that health professionals should be following, available here.