South Africa's annual population growth rate, in the traditional sector, is 3.5% (1980- 2000), a rate similar to those experienced in the rest of sub-Saharan Africa, and over which the World Bank has expressed concern. For the purposes of this study, economic factors explaining family size choice in the traditional sector were examined and linkages between family size decisions and socio-economic variables analysed. Household utility was maximised subject to resource constraints of time, labour and income, from which a demand curve for children was derived with emphasis on the opportunity cost of wives' time and the quantity-quality trade-off for children. A stratified sampling technique was used to collect data from KwaZulu households in South Africa. Regression analysis was used to estimate the demand function and principal components analysis confirmed the underlying theoretical linkages. Results show that wife's education (expected income or opportunity cost), child help (benefits) and desired family size were important explanatory variables. Three components extracted represented the substitution effect, the income effect and child investment theory. Results show that investment in education, taken as a proxy for expected earnings, is a strong policy option for reducing family size.