What Causes Nose Bleeds In A Child?

hi this Q is for my son who is 6 years old we feel he has adinode problem he falls sick often may be 15 to 30 days intravel he was on treatment in you hosptial under Dr subba rao & Slyn intialiy treated for Brancho asthma now we are finding him bleeding through nose often we had told about this to doctor but we are worried since this happen since school.