How to distinguish between viral and bacterial sinus infection in children?

Sinuses are 4 : sets of air-filled, mucous membrane-lined pockets near nasal passages that don't develop fully until adolescence. 2 sets are small, but present at birth; 1 set begins to develop at 7 yrs. & 1 in adolescence. Suspect bacterial sinusitis in a child with a 10-14 day history of viral or allergic nasal congestion, fever, green nasal discharge & headache. See www.entnet.org/content/pediatric-sinusitis.