 Child labour refers to the employment of children in any work that deprives children of their childhood, interferes with their ability to attend regular school, and that is mentally, physically, socially or morally dangerous and harmful. This practice is considered exploitative by many international organizations. Legislation across the world prohibit child labour. These laws do not consider all work by children as child labour. Exceptions include work by child artists, family duties, supervised training, certain categories of work such as those by Amish children, some forms of child work common among indigenous American children, and others. Child labour has existed to varying extents, through most of history. During the 19th and early 20th centuries, many children aged 5 to 14 from poorer families still worked in Europe, the United States and various colonies of European powers. These children mainly worked in agriculture, home-based assembly operations, factories, mining and in services such as newsboys. Some worked night shifts lasting 12 hours. With the rise of household income, availability of schools and passage of child labour laws, the incidence rates of child labour fell. In the world's poorest countries, around one in four children are engaged in child labour, the highest number of whom 29% live in sub-Saharan Africa. In 2017, four African nations Mali, Benin, Chad and Guinea-De-Sau witnessed over 50% of children aged 5 to 14 working. Worldwide agriculture is the largest employer of child labour. The vast majority of child labour is found in rural settings and in formal urban economy, children are predominantly employed by their parents, rather than factories. The majority and lack of schools are considered as the primary cause of child labour. Globally the incidence of child labour decreased from 25% to 10% between 1960 and 2003, according to the World Bank. Nevertheless, the total number of child labourers remains high, with UNICEF and ILO acknowledging an estimated 168 million children aged 5 to 17 worldwide, re-involved in child labour in 2013.