July actually has been hotter than August for the last several years (although, subjectively, August feels more oppressive because by then it's been so hot for so long). June is better than either.

August is definitely the worst of the summer months in terms of heat. June and July should be a little better, especially if they're doing a water based activity (I'm not sure what ages your kids are, but I know the older ones stick to one activity the whole week).

We are new to the area. My kids did Calleva MD last August, and it seems they were always very hot and surrounded by bugs. Would it be any better if we booked those camps in June or early July? What part of the summer does the weather/buginess really start to get unbearable?