A grim truth underlies U.S. industry: the appalling practice of child labor, widely perceived as an anachronism, is far from a thing of the sooty industrial past. U.S. consumers may have a hazy sense that children labor somewhere in foreign sweatshops to manufacture their goods — but such faraway tragedies are too easily forgotten at the checkout.

But child labor persists domestically as well. Because the practice has long been obscured from view, recent exposures of its real scope have elicited public surprise. In the past year, journalistic and governmental investigations of Southern manufacturers turned up systematic violations, while in February, The New York Times published a powerful exposé that highlighted migrant children who’d been steered into grueling work in manufacturing and agriculture. Still, these were mere glimpses. In the last fiscal year alone, the Department of Labor discovered 835 companies illegally employing more than 3,800 minors.

Those figures are startling enough — but the actual extent of legal U.S. child labor is truly vast. At present, enormous numbers of minors, many of them migrant children, are legally employed […]