Leprosy is an infectious disease with an average incubation period of two to five years. It is caused by Mycobacterium leprae, mainly affecting skin, mucous membranes and peripheral nerves. When it occurs in children under fifteen, it reflects an intense and long contact period, with a high bacillary load. Therefore, it is considered an important alert sign that points to the challenge of controlling the disease. The authors report three cases of leprosy in children under fifteen that occurred in the Itaguaí district, Rio de Janeiro. The epidemiologic implications of new cases detected at this age and the fundamental role of examining the patients' close contacts and the possible identification of source cases as an effort for leprosy control are discussed.