Sudden fatal cases of influenza B infection in a 4-year-old girl and a 2-year-old boy are presented. Both children complained of abdominal pain without respiratory, neurologic or cardiac symptoms; additionally the girl had vomiting within 2 days of death. Autopsy revealed histological changes in the respiratory system consistent with a viral infection. Influenza B infection was identified by immunohistochemistry in the girl and real-time polymerase chain reaction in the boy. Additional testing including cultures, toxicology, and screening for metabolic disorders were negative. These cases illustrate the usefulness of viral testing, especially for influenza, in the medical legal autopsy of children even when the classic respiratory symptoms of flu are lacking.