This open-label randomized 2 arm study will determine the emergence of viral resistance in participants with seasonal influenza A infection treated with oseltamivir. Eligible participants less than or equal to (</=) 5 years of age will be randomized to receive oseltamivir at either standard dose (30-75 milligrams [mg] orally twice daily [bid]) or double dose (60-150 mg orally bid) for 5 days. Target sample size is greater than (>) 100.