Sinusitis, or sinus infection, is an inflammation caused by a bacterial infection of the cavities within the facial bone. Contrary to what you may hear, this illness is quite rare. It is even rarer in younger children, for the simple reason that their sinus cavities are not yet fully formed and therefore cannot be infected. Sinusitis usually includes a significant fever and a thick, persistent nasal discharge in school-age children. Other possible complaints include headaches and a sense of fullness in the face, but these are not reliable symptoms in young kids. Your doctor will treat sinusitis with antibiotics.
Lingering colds with persistent mucus production are often mistaken for sinusitis and treated unnecessarily with antibiotics. This is not appropriate, even if the mucus turns green, which is normal at the end of a cold.