The official website of the Parliament of the United Kingdom states that the Mines Act of 1842 was a piece of legislation introduced to ensure that boys under the age of 10 were prohibited from being used as labor in coal mines. The act was hastily enacted, and subsequent legislation increased the minimum age for boys in the coal mines from 10 to 12.
According to the Encyclopedia Brittannica, Anthony Ashley-Cooper, the seventh earl of Shaftesbury, who briefly served on the General Board of Health, championed the Mines Act when his investigatory visits to British coal mines revealed that children as young as four and five were working in the shafts. A Web of English History explains that the Mines Act prohibited all females, adults and children, from being used as underground mine workers at all. Due to the fact that the Mines Act was imposed on an emergency basis and not fully formed, there were no restrictions on hours for child workers over the age of 10. Parliament notes that further legislation both in 1850 and 1860 introduced additional regulations on mine safety, improved working conditions, and increased the age limit for boys working underground from 10 to 12.