How do i know if my child has the the real flu virus?

May be difficult: Rapid influenza testing by nasal swab, viral cultures, or retrospectively by serologic testing. There are many viral infections which can mimic influenza, inclluding parainfluenza, some adenoviruses, and so on and so on. Generally influenza will be active in the community and doctors, having been informed of this by the health departments, will have high indices of suspicion.