In the early twentieth century, child labor was a pervasive phenomenon. Studies estimate that between one-fifth and one-sixth of all children were employed on a full-time basis, and child labor was an important economic factor. Instead of attending school, proletariat children worked as much as sixty hours per week in unsafe factories and coalmines. Few child labor laws protected the children from the hazards of their workplace, or from the exploitation of the factory owners. The situation was especially appalling in the textile mills, where children worked near powerful machinery that left many of them severely injured and maimed.
When a strike began in the textile mills of Kensington in Philadelphia, Mother Jones vowed to expose the crimes of child labor. The Textile Workers Union had demanded that the work-week decrease from sixty to fifty-five hours, and that women and children be prohibited from working night hours. Mother Jones convinced the leaders of the strike to prioritize the issues related to child labor, then devoted all of her energy into publicizing this campaign. She organized a children's march from Philadelphia to New York. The march, which was made up of roughly two hundred children and supporting workers, took place over several weeks. Mother Jones made frequent stops to give speeches and to show the public the effects of exploitation–many of the children marching were permanently maimed, which provided real proof of the dangers of their employment. Mother Jones gained much publicity for the plight of child laborers, but the strike itself was not successful. Nonetheless, the march was an important first step toward the government's eradication of child labor in the United States.
After the Children's Crusade, Mother Jones worked for the Illinois Socialists, giving speeches and holding rallies. She continued to organize workers, traveling widely to the most desolate regions to support workers on strike. In her speeches, Jones espoused a radical idea of class-consciousness that crossed ethnic and racial boundaries. She avoided, however, the ideological debates that many socialist intellectuals indulged in. Even after several bouts of pneumonia, Jones continued to proselytize. She spoke the jargon of the miners, and was able to translate the doctrines of socialism from an ideological abstraction to a concrete reality. Jones also participated in the formation of the Industrial Workers of the World, a radical labor organization which emphasized industrial organization as opposed to electoral politics. The IWW was based on industrial unionism instead of craft unionism. Some of the leaders of the WFM, such as Bill Haywood, also participated and became active members of the IWW, which opposed the more conciliatory tactics of cooperating with business, which some labor organizations espoused.
Mother Jones also campaigned against the dictatorial Diaz government in Mexico, which imprisoned and tortured radicals, and was a persistent violator of human rights and civil liberties. The Partido Liberal Mexicano (PLM), a radical group that opposed the Diaz government, was especially targeted, and many of its leaders fled to the United States. In 1907, four of these leaders, who had been staying in Los Angeles, were arrested. Between 1907 and 1910, Mother Jones campaigned furiously on their behalf, raising money for their defense. After serving prison sentences, the four leaders were finally released in 1910, and a new government was installed in Mexico. Although the new government was not revolutionary, civil liberties were granted, and the new president favored the right to organize unions.