PHOTO: LIBRARY OF CONGRESS

In the 19th century, factory owners discovered children could run their machinery for a fraction of what adults would cost. By 1900, 2 million children were working 12 to 18 hours a day, with up to 35,000 dying annually on the job. Combatting this social scourge was the National Child Labor Committee's exhibit at the 1915 Panama-Pacific International Exposition in San Francisco. Rich informational displays prescribed compulsory education, child-labor laws, and improved health care. The exhibit helped pave the way for the 1938 Fair Labor Standards Act, which barred the employment of most minors.