There's some bed wetting medications that doctors can prescribe to help prevent your child from bed wetting.
Have your child avoid any liquids an hour before bed and make sure he goes to the restroom 2 hours before going to bed and again when he goes to bed.
This helps to get his bladder emptied and an empty bladder leaves more room for more urine lessening the chance of him wetting the bed.
Set an alarm clock for yourself and get him up during the middle of the night so he can urinate.
You might also try using diapers for his bed wetting if he'll wear them.