Viral Conjunctivitis: This is the most common cause of conjunctivitis in children, often presenting with goopy eyes due to viral infection, commonly adenovirus. The age of the child and the symptoms align well with this diagnosis.

Bacterial Conjunctivitis: Caused by bacteria such as Staphylococcus aureus, Haemophilus influenzae, or Streptococcus pneumoniae, it presents similarly to viral conjunctivitis but may have a thicker, more purulent discharge.
Allergic Conjunctivitis: Though less common in this age group, it can occur, especially if there's a history of allergies. Symptoms include itchy, watery eyes, and stringy discharge.
Chlamydial Conjunctivitis: Inclusion conjunctivitis caused by Chlamydia trachomatis can occur in children, especially if the mother has an untreated chlamydial infection. It presents with chronic conjunctivitis and can have a significant impact if not treated.

Gonococcal Conjunctivitis: Caused by Neisseria gonorrhoeae, it's a rare but serious condition that can lead to corneal perforation and blindness if not promptly treated. It's crucial to consider this in any child with severe conjunctivitis, especially if there's a suspicion of sexual abuse.
Herpes Simplex Virus (HSV) Conjunctivitis: HSV can cause a severe form of conjunctivitis and keratitis. Early recognition and treatment are critical to prevent long-term vision loss.

Kawasaki Disease: Though primarily known for its systemic symptoms like fever, rash, and lymphadenopathy, Kawasaki disease can also present with bilateral nonexudative conjunctivitis. It's rare but important to consider due to its potential for cardiac complications.
Sjögren's Syndrome: An autoimmune disorder that can cause conjunctivitis among other symptoms. It's exceedingly rare in children but should be considered in those with persistent symptoms and systemic findings suggestive of an autoimmune disorder.