Higher fertility in developing world is partially explained by large number of hand needed to perform work. Explain me this line?

• Fertility rates tend to be higher in poorly resourced countries.
• In developing countries, children are needed as a labour force and to provide care for their parents in old age.
• More the number of children, more will be the number of working hands which would contribute to the family income.
• In developing countries, fertility rates are higher due to the lack of access to contraceptives and generally lower levels of female education. 
• The social structure, religious beliefs, economic prosperity and urbanisation within each country are likely to affect birth rates as well as abortion rates.