The main source of HIV infection in young children is of their mothers, during pregnancy, labor and delivery, or by breastfeeding. The rate of HIV transmission from infected mothers to their newborn children varies from 15% to 40% with one-thirds of these infections was through breastfeeding. This paper examines cross-sectional population-based survey data of HIV test results among mothers and their children in Uganda, Swaziland to estimates of mother-to- child transmission (MTCT) rate of HIV infection. The prevalence of HIV among women aged 15 - 49 who gave birth in the past 5 years in Uganda is 7.3%, and in Swaziland is 37.9%. The HIV prevalence of children who mothers were HIV positive were very similar: 10.3% in Uganda and 11.5% in Swaziland. This association represents the crude rate of MTCT in these two countries at the time of the survey. Presence of HIV antibody in early age (0 - 11 months) is due to both true infection and passive antibody from mothers. The seroconversion dropped nearly half in the second year of age which was likely that many of these children died before reaching the age of 12 - 23 months and passive antibody were gradually cleared at this point. This analysis demonstrated that cross-sectional data can be used to estimate indirectly the magnitude and dynamic of MTCT.