Bed wetting problems?

I have a 5 almost 6 year old that was completely potty trained for almost a year. He is very sensitive to change. And when his mother moved a few months ago he had a couple of accidents. I looked ped this but his mother started putting diapers on him again.He said that it is ok now because he is wearing a diaper so he doesn't have to get up. Now he is wetting the bed nightly. I know that he can go through the night without wetting. What do I do? Do I punish him? Do I just give it time.