U.S. officials said the Labor Department had seen a nearly 70% increase in child labor violations since 2018, including in hazardous occupations.
In the last fiscal year, 835 companies were found to have violated child labor laws.
It has created an interagency task force on child labor, and plans to target industries where violations are most likely to occur for investigations.
The Hearthside investigation is the latest in an uptick of similar probes.
Reuters last year published a series of stories on child labor including revelations about the use of child labor among suppliers to Hyundai, including a direct subsidiary of the Korean auto giant, in the U.S. state of Alabama.