Thank your for your query,
Nose bleeding in child with flu
is due to bleeding from the weak portion of the nasal cavity
You can stop the bleeding by firmly pressing the bleeding side nostri and holding it for some time against the nasal bridge.
This method stop bleeding and only one nostril
should be pressed at one time to allow the breathing from the other nostril.
If bleeding continues inspite of this method then consult your doctor or emergency.
Hope i have answered your query.