More than 100 teenagers, ages 13-17, worked for Packers Sanitation Services, the Department of Labor said.
The agency called it a “systemic” failure by the company.
National laws bar employment of children under the age of 14 and limit the hours teenagers can work.
A spokesperson for Packers Sanitation Services said the firm had a “zero-tolerance policy” against employing anyone under the age of 18 and had conducted multiple audits and additional training after it became aware of the allegations.
Many of the people identified by officials had left the firm “multiple years ago”, the spokesperson added.
“We are fully committed to working with [the Department of Labor] to make additional improvements to enforce our prohibition of employing anyone under the age of 18,” they said.
The settlement resolves an investigation that the Department of Labor started last year.
It found at least three teens were injured on the job, which involved using hazardous chemicals to clean equipment such as back saws and head splitters.
Officials said the firm had overlooked internal flags and that some managers later tried to obstruct the inquiry.
“The child labour violations in this case were systemic and reached across eight states, and clearly indicate a corporate-wide failure by Packers Sanitation Services at all levels,” said Jessica Looman, principal deputy administrator at the Department of Labor’s wage and hour division.
“These children should never have been employed in meat packing plants and this can only happen when employers do not take responsibility to prevent child labor violations from occurring in the first place,” Ms Looman said.
The teens worked across eight states at 13 plants of major firms.
The roughly $15,000 (£12,400) penalty per person was the maximum allowed, officials said.
Teen employment fell in the years after the 2008-2009 financial crisis, as job creation remained relatively weak. But it has increased sharply since the pandemic, as employers scrambled to find workers.
Last summer, the Department of Labor expressed alarm about a rise in child labour violations in the US.
In 2022, the agency handled more than 800 cases of child labour violations involving nearly 4,000 minors, up sharply from 2015.
US child labour rules bar employment of those under the age of 14. Teens ages 14 and 15 cannot work later than 7pm during the school year or past 9pm over the summer.
Laws also prohibit them from working more than three hours on school days, more than eight hours on non-school days and more than 18 hours per week.