My son had accidents at night until he was 12 years old. It was very frustrating, because of spending the night with friends or going to camp or traveling. My pediatrician says it is not really considered an issue until they are 8 years old and not considered a serious concern until after age 12. It is somewhat common, especially with boys.
My son had less accidents as he got older and would even go for several months without an accident and I would think, "YEA!" we are done and then it would start again. Sometimes he would go a week or two dry and then have accidents 3 or 4 nights in a row. I could not find any rhyme or reason to it! Even on nights when his dad would buy him a huge Icee on the way home from an activity, I couldn't be sure if he would have an accident or not! (I always told my husband on those nights, YOU have to change the sheets!)
At age 6, he is still pretty young and it is very common at this age. My son was also a very hard sleeper also. At that age, he would often not even wake up when he wet the bed. If your son can wear the pull-ups, then that is helpful, but can get kind of expensive over time. I know my nephews had to wear pull-ups until their teens! My son hated to wear the pull-ups (didn't even like to wear underwear until we started using boxers) and the boxer type pull-ups would leak. Since it he did not wet the bed every single night, just once or twice a week, I didn't make him wear the pull-ups. I just put a heavy waterproof mattress protector on his bed and also bought a waterproof pad that was like a big rectangle, maybe more of a crib pad. I would put a sheet over the mattress protector and then the big loose rectangle pad and then a second sheet over that. That it made it easier to change the bed in the middle of the night. Just take the top sheet and pad off and you already had a dry sheet underneath. I also used this loose mattress pad when we traveled. I think a time or two I even bought some disposable waterproof pads to use in hotel rooms.
As my son got older, it did happen much less frequently, but it was still a problem. I don't remember for sure how old he was (definitely after age 8) that my doctor gave him a pill to try. One of the problems can be that they are not producing enough of a hormone that shuts down their urine production during sleep. He took this pill for a month or so and it worked like a charm! Unfortunately, you can't stay on it indefinitely. But it was obvious that this was the problem and as soon as his system matured and produced enough of the hormone on it's own, then he didn't have any more accidents. The hope is that by taking the pill for a while, it will jump start the system or retrain them to stay dry. We would try this treatment once a year and I chose to do it in the summer, so that he could go to church camp and on vacation and to spend the night with his friends. My pediatrician also suggested the alarms, but we didn't really want to try that.
My son is a great kid and I hated for him to go through this. Never any discipline problems and such a sweet and loving child. Please do not blame your son or make him feel bad about this problem, because he can not control it. It can be really humiliating for them and your understanding is really needed. It is hard not to get really frustrated with the constant washing and be awakened in the night. As my son got older, we worked out a system to make it easier for both of us. He had a sleeping bag on the floor in his room and so if he had an accident, he just got up and changed his clothes and went back to sleep on the sleeping bag. He didn't have to wake me up or disrupt his sleep by trying to change sheets during the night.
Hopefully, your son will outgrow it in a year or two. Most kids do. But if your son if one of the unlucky ones like my son, then you need to help and support him.