“Helpers at the nest,” young adults remaining in their parents home to take care of younger siblings, are known in many species of birds and mammals. Similar behaviors are occasionally observed in human societies but their frequency and significance for parental reproductive success are still not fully appraised. This study was designed to document this issue in a traditional Aymara peasant society of the Bolivian Altiplano, It is based on 359 reproductive life histories of women 45 years of age or older and on a survey of children's workload in 1998 and 1999. The presence of “potential helpers” in the household is significantly associated with higher fertility and with improved survival of siblings to sexual maturity. Caretaking is not particularly assigned to older daughters. The positive relationship between the availability of offspring help and reproductive success does not demonstrate a causal role for child caretaking because, in contrast with nonhuman helpers, workloads of children range from housekeeping to agricultural tasks, instead of being focused on feeding or protecting younger siblings. Correlation and multiple regression analyses, however, suggest that the total amount of care given by the older offspring and the amount of care received by each recipient are, along with offspring contribution to household economy, among the determinants of parental reproductive success. Am. J. Hum. Biol. 14:372–379, 2002. © 2002 Wiley-Liss, Inc.