Prevention of bed wetting?

My niece wet the bed until she was 15, everything was tried the Dr., no drinking after a certain time, went to the bathroom before bed, she was woke up in the night to go, and she would still wet sometimes. Only she would get in trouble because my brother was being an a**. she grew out of it and now her youngest son does the same thing they have pull ups big enough for 7 year olds and he wears on every night just in case. Most kids grow out of this. Don't give him medicine.