Children can play a variety of roles in emerging infectious diseases. They can be victims, as in the vertical transmission of human immunodeficiency virus infection. They can be affected in a minor way compared with adults, as in West Nile virus infection, legionellosis, and coronavirus infection leading to severe acute respiratory syndrome (SARS). Sometimes, however, they play predominant roles—sources for other age groups—as do toddlers in out-of-the-home child care for transmission of penicillinresistant pneumococci and cytomegalovirus to family members. Children have a uniquely central role in transmitting the influenza viruses that cause annual seasonal outbreaks and epidemic disease and could cause global epidemic (or pandemic) disease. Children themselves suffer excessive morbidity and mortality from influenza. Continuous minor changes in virus neuraminidase and haemagglutinin components (antigenic drift) or a major change in either (antigenic shift) render naïve children especially vulnerable. Anticipating that pandemic influenza could occur at any time because of a major change in a human strain of influenza virus or through acquisition of human transmissibility of reassortant avian influenza strain(s) (Nicholson et al., 2003), the international community of healthcare experts are collaborating increasingly, and countries are drafting influenza pandemic preparedness plans. A draft by the U.S. Department of Health and Human Services of “Pandemic Influenza Preparedness and Response Plan” was released for comment in August 2004 (http://www.hhs.gov/nvpo/pandemicplan). All plans highlight the critical importance of international surveillance, openness, and rapid response to investigate and contain emergent avian or human strains.