I have friends who had a very laid back parenting style. They often left their children home alone for a few minutes, and in varying combinations -- their girls were like 10, 6, 4, and 2 (maybe 7, 5, and 3?).
One day, after many times of having done this safely, the girls having called their parents safely, etc., they went to their storage shed a couple miles from their house, and the two middle girls wanted to stay home. On this particular day, the older girl changed her mind about staying home and decided she should walk to the storage center.
She was picked up by an officer during the walk, and you can guess what they went through next -- not to mention, she left her younger sister at home alone.
This was a mature, capable, lovely girl who had shown herself to be responsible on many occasions. It's easy to say "My child wouldn't do that." These parents didn't believe their child would do that.
I simply would not do it. What-if's aside -- the "what if child protective services took my children into the care of strangers" is too great of a what-if. It doesn't have to be mandatory reporting at school. It could be a friend, a friend's mother, a doctor, a neighbor. And asking your son to be secretive about it sounds psychologically harmful to me -- it gives him the idea that it's wrong, and he has to keep it secret to keep himself and you safe.