To determine which condition is associated with conjunctival injection, pharyngeal injection, polymorphic rash, and cervical lymphadenopathy, let's analyze the options:
- Kawasaki syndrome: Kawasaki syndrome is characterized by symptoms such as conjunctival injection, cracked lips, polymorphic rash, and cervical lymphadenopathy, among other symptoms. It primarily affects children under 5 years old and involves systemic vasculitis.
 - Measles: Measles commonly presents with a maculopapular rash and Koplik spots in the oral cavity, but conjunctival injection and cervical lymphadenopathy are not the primary features.
 - Thrombocytopenia: This condition primarily involves a low platelet count leading to bleeding and bruising, and does not typically present with conjunctival injection or the other listed symptoms.
 - Mumps: Mumps is characterized by parotid gland swelling, fever, and sometimes meningitis, but does not primarily cause conjunctival injection or a polymorphic rash.
 
Based on the analysis, Kawasaki syndrome is the condition that fits all the symptoms listed: conjunctival injection, pharyngeal injection, polymorphic rash, and cervical lymphadenopathy.