The Canadian wildfires that have shrouded much of the nation in smoky haze are making it much harder for American kids to enjoy one of the staples of summer camp: fresh country air. As a result, many camps in the Midwest and the East have been moving activities indoors, seeking advice from medical professionals and hoping the air quality improves soon so campers can get back to hiking, playing tetherball and waging games of capture the flag. “There’s certainly a concern, considering that we take children from the cities,” Mark Zides, chairman of the Pennsylvania Camp Association, said Thursday.