This paper presents the preliminary results from my research focused on beliefs and practices related with the life cycle and certain health-illness processes related to their different stages, in two Mbya communities in the province of Misiones, in the Argentinian northeast. We have centered our research on parasite illnesses and the groups’ numerous beliefs and experiences around their origin, diagnosis, prevention and therapeutics. Starting from the results obtained from an interdisciplinary research project on enteroparasitosis in these aboriginal communities and my work within the framework of some ethnographic research that has been developing since 1996, we set out to approach their knowledge and practices around gastrointestinal diseases mainly affecting child population, in the context of the group’s everyday life. Systematic observation was made of the activities performed by different sex and age members in several domestic units of these communities, in order to characterize the diagnosis, treatment and prevention strategies performed by different individuals as well as recognize and define risk situations related with parasite infestation and transmission in the context of their domestic activities. Likewise, open-ended interviews were made to adults of both sexes – laymen and local experts - in order to access to the group’s categorization and definition of the lifecycle, as well as investigate into the health- illness processes associated to their different stages. Our investigation showed that certain forms of child care, in particular those related to respecting food prescriptions and taboos are meant to protect children from possible risk situations. Analysis and assessment of this information lead us to propose certain hypotheses about the connection between these practices and different environmental factors in terms of the prevalence of these illnesses during the first stages of life.