One of the greatest incentives behind the reason why people who live in the least industrialized nations have more children is

In the past and during the first industrial revolution of the late 18th and early 19th century, a decline in child birth rates came as factories we're created. Before the industrial revolution more kids meant more help on farms. In civilizations where goods are created in the homes of the people and not industrialized people will have more children to create more employees essentially.