The purpose of this study is to assess the safety and immune response (body's defense against disease) to an experimental H1N1 influenza vaccine against the 2009 H1N1 virus. This study will help determine how and when the H1N1 flu shot should be given with the seasonal flu shot to make it most effective. The 650 participants will be divided into the following age groups: infants from 6 months-36 months old, children 36 months-9 years old, and adolescents 10-17 years old. Each age group will have 200 children. There are 4 treatment groups in each age level. Study procedures include: medical history, targeted physical exam based on history, maintaining a memory aid, and blood sample collection. Participants will be involved in the study for about 8 months.