What are the limits of childhood? When does it start and when does it end? Does it happen at the same time for girls and boys? What impact do physiological processes have? What impact do social institutions such as the school have? These questions, all too familiar to many childhood researchers, emerged again when researching menstruation in four different regions of Peru. This paper focuses on one of them, Ucayali, where I reconsider research conducted in previous years in different communities in the light of more recent work. The aim was to examine the characteristics of childhood among the Shipibo people, with a particular focus on girls, and how a biological process such as menstruation implies social representations and actions, and reflects gender norms. Results show an imaginary in which sexual maturation and the possibility of being a mother signals the end of childhood, entering a period of danger and the need for greater control, which is not present for boys of the same age group. Since this is such a defining process, there is a strong lack of information on menstruation among girls, as well as gaps and silence in school that contribute to the reproduction of such a lack of information. Fear and embarrassment, fuelled by lack of information, reduce girls’ assistance or restrict their participation in the school when menstruating, which in turn negatively affects school experiences and learning, reproducing and strengthening gender inequalities during childhood.