The process of industrialization process was too much developing during the starting period of 19th century. The children were employed because the owners of the factories can given them low wages and even they don't even need to provide them more place to live and even food to eat. Therefore children were forcefully employed in factories.  
Industrial revolution first began in Britain,European countries.and there were lots n lots of factories established there(london).and to run these industries the owners need labours and workers to do the work so they started employing men,women and even children too.bcoz of the lack of workers they started employing children so that they won't be asking for more wages,and they only need small amount of food to eat and place to the owners employed children and made them to carry heavy loads,to do much work and these owners used to torcher the children to do work for 19hrs per day and they would get small amount of food for the heavy they employed children for their advantages like-children require small amount of food,and less wages and they'll just listen to what the owners say etc.... Hope this helps.pls mark as brainliest....
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