**Core Concept**
The case presents a child with joint swelling and pain, preceded by an upper respiratory infection, which is a common presentation of a condition involving autoimmune and inflammatory components. The presence of a petechial rash and bleeding per rectum suggests a systemic manifestation of the condition.

**Why the Correct Answer is Right**
The child's symptoms are suggestive of Henoch-Schönlein Purpura (HSP), a form of vasculitis that primarily affects small blood vessels. It is characterized by the deposition of IgA immune complexes in the affected vessels, leading to inflammation and damage. The condition often presents with a triad of symptoms: non-thrombocytopenic purpura, abdominal pain, and joint inflammation. The petechial rash and bleeding per rectum are indicative of the gastrointestinal and renal involvement, which are common in HSP.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because Kawasaki disease typically presents with cervical lymphadenopathy, conjunctival injection, and mucocutaneous lesions, which are not seen in this case.
**Option B:** This option is incorrect because Juvenile Idiopathic Arthritis (JIA) primarily presents with joint inflammation and does not typically have a petechial rash or bleeding per rectum.
**Option C:** This option is incorrect because Sickle Cell Anemia presents with episodes of pain crisis, which are usually related to vaso-occlusive events, and not typically preceded by an upper respiratory infection.

**Clinical Pearl / High-Yield Fact**
HSP often presents with a prodromal phase characterized by upper respiratory tract symptoms, followed by the development of rash, joint pain, and gastrointestinal symptoms. It is essential to recognize the classic triad of symptoms to diagnose HSP early and initiate appropriate management.

**Correct Answer:** C.