There are studies and I may or may not find them later.
High birth rates contribute to overpopulation in many developing countries. Children, especially boys, are assets to many poor families because they provide labor, usually for farming. Cultural norms in traditionally rural societies commonly sanction the value of large families. Also, the governments of developing countries often provide little or no support, financial or political, for family planning (see Birth Control) Families may also not know about family planning due to the lack of education. Hence, most developing countries have high rates of population growth.