The World Bank has expressed concern over high population growth rates in sub-Saharan Africa. South Africa's annual population growth rate in the traditional sector is 3,5%. This study identifies economic factors affecting family size choice to provide policy makers with a strategy for reducing fertility. A neoclassical utility framework was used to analyse linkages between family size decisions and socio-economic variables. Household utility for "child services" and "standard of living" was maximised subject to the resource constraints of time, labour and income. A demand curve for children was specified within a simultaneous model of family decision making. A stratified sampling technique was used to collect household data from Ulundi and Ubombo in KwaZulu. One hundred and seventy five women in three equal occupational strata were interviewed. The simultaneous model was estimated by two-stage least squares regression analysis. Dummy dependent variables were estimated by probit analysis. Child education, women's opportunity cost of time and formal market participation were negatively related to fertility, rcnecting substitution from numbers of children (time intensive goods) to fewer, more educated children(less time intensive) as opportunity costs rise. Child labour was positively related to fertility. Strategics to reduce population growth rates should therefore include improvements in women's education and employment opportunities to raise their time costs, and time saving devices to reduce demand for child labour.