Your child's pediatrician can do some tests on your child for his bed wetting.
But most times bed wetting in children is due to just growth problems with the bladder.
Basically the bladders is not growing as fast as it should with the child's body and the bladder is weak so the bladder overfills before the child is able to wake up and go to the bathroom.
Most children will outgrow bed wetting by 15 or 16 years of age at the latest.