I slept walk from the time I was about 7 until highschool. I walked outside once with my blanket in my hand and walked down the driveway toward the street. When my mother retrieved me I told her I needed to help our neighbor (that lived behind us, not in the direction which I was going!). I was in fifth grade at that time.
I remember all of my sleepwalking episodes, strangley enough. The last one I remember was my freshman or sophomore year and my dad and brother were talking in the room next to mine and I awoke and told them that my father's friend owed me money...it was weird! But it made sense to me at the time. My parents just always had me go back to bed and never really took any other precautions (that I'm aware of).
I've never had another episode since. There have been times that I have conversed with people in my sleep and have no recollection of it the next day (this has happened with roommates that woke me up or with my husband). Whatever safety precautions you need to take should be done..is there some kind of alarm that can go on the door of your son's room should he wake up and leave it in the middle of the night? I really don't have any other suggestions, just wanted to let you know that it did eventually go away and it wasn't a regular occurence. Good luck with your son!