I am not even sure why you should brother to ask here, by the way, I think there are many scientific studies out there on the internet about this matter and they gets to almost the same conclusions.
Women in under-developed countries do not have access to both sexual education nor birth control pills, so it is more likely for them to have an unwanted pregnancy. Also, having more children in a underdeveloped country can be helpful to face hardships, specially in the children grow up to become healthy men, so they can contribute to society and bring back some some money and food to sustain the household. There is a good reason in under-developed countries family members live close to one another, you know. So they can band together to survive.