There are drugs available to suppress urine production at night time. Although they have only minimal side effects, I would not recommend drugs as the first line of treatment. There are behavioral therapies in medicine that could help your kids, failing which drugs could be used.
Next Steps
The best person to visit would be a pediatrician or if possible a pediatric psychiatrist/ psychologist. They'll teach you the behavioral therapy that is needed in cases of recurrent bed-wetting.
Health Tips
Teaching kids to void their bladder before sleep should help significantly and avoid any further consultations.