Without a warrant, they'd have a very difficult time finding evidence that it's a sleepaway camp and not day camp.
-1
Wouldn't there be dozens (or hundreds) of delivery trucks, repairmen, etc over the summer who would all enter camp and see exactly what's going on? And not to mention neighbors and people from the surrounding towns being on high alert- they'll know in a second.
It'll be all over social media in no time, in the press shortly thereafter (news-hungry reporters at the camp entrance eager for a juicy story), and on a desk in whatever police dept enforces this stuff not too long after. And then can't the police just get a warrant?
I think it's highly unlikely (practically impossible) that any camp can stay under the radar for more than a few days with hundreds of kids.