Not only in Africa this also happens in my country, families that are living in remote areas usually have an average of 6 children and this is due to ignorance, the family tradition that a big family has a good reputation in the community and of course they are hoping that their children will get them out of poverty, its like an endless cycle.
This is not always the case, many couples are now matured and the government are educating them on having a small family, so they can manage the household and the health of all the members of the family.