Between one and two million migrants reside in cramped conditions in Nairobi’s slums without proper access to sanitation or affordable clean water. Children in such areas are exposed to enormous risks, health risks in particular. Using longitudinal data collected every four months during the period between 2002 and 2004, we analyze their survival patterns of children under five year of age who resided in two informal settlements (Viwandani and Korogocho). The research question assumes that children born to recent migrant mothers are more likely to die. The assumption is that migrant mothers do not have social network, which translates to a lack of information and lower access to health facilities. In the subsequent event history analysis, childhood mortality is shown to remain very high in the Nairobi informal settlements, especially among new migrants. Given the high degree of rural urban migration, which is bound to increase in the foreseeable future for most African countries, our study raises critical public health concerns. Another important finding in the context of the HIV AIDS pandemic is the risk factor associated to the mortality among children who have lost their mother. Our study also demonstrated a persistent disadvantage of children born to migrant mothers irrespective the length of stay in the receiving zone. The latter seems to point out the difficulties for migrant to develop social network outside their area of origin.