This act was instigated by a report from a Royal Commission on women and children in coal mines. The report came back and caused widespread public dismay and horror. It was discovered that coal mine owners had a great lack of concern for their workers. Frequently, children aged 8 were found working underground in the mines, but there were some even younger. The report also had graphic images of women and children working in the mines. It was passed in 1842 very quickly and hastily by Parliament. The act prohibited all underground work for women and girls and boys under the age of 10.
This act was supported greatly by Anthony Ashley-Cooper, the 7th earl of Shaftesbury.
"Coal Mines." UK Parliament, UK Parliament. https://www.parliament.uk/about/living-heritage/transformingsociety/liv…