Which of the following is the most common cause of orbital cellulitis in children?

Orbital cellulitis in children is most commonly caused by a sinus infection, particularly the frontal or ethmoid sinuses. This condition arises when bacteria from an adjacent infected sinus penetrate the orbit, leading to inflammation and infection of the soft tissues surrounding the eye.

In children, sinus infections are prevalent due to their anatomical and physiological characteristics, such as the size and development of the sinuses. The proximity of the sinuses to the orbits means that any infection in the sinus can easily spread, making it the leading cause of orbital cellulitis in this population.

Other potential causes, like facial trauma or dental infections, can lead to orbital cellulitis but are less common compared to the direct spread from a sinus infection. While viral infections can also cause orbital inflammation, they are more likely to produce a different clinical picture, such as viral conjunctivitis, rather than classic orbital cellulitis. Thus, sinus infections are the primary concern when considering the etiology of the condition in young patients.