**Core Concept**
The child's presentation is suggestive of a vasculitis, specifically a small vessel vasculitis, characterized by deposition of IgA immune complexes and neutrophilic infiltration.

**Why the Correct Answer is Right**
The presence of perivascular IgA deposition and neutrophilic collection is indicative of Henoch-Schönlein purpura (HSP), a small vessel vasculitis. HSP typically affects children and is characterized by the deposition of IgA immune complexes in the affected vessels. The erythematous rash on the lower limb and non-blanching purpura are classic clinical findings in HSP. The involvement of IgA immune complexes suggests an abnormal immune response, leading to the activation of neutrophils and subsequent inflammation.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because HSP is not typically associated with the deposition of IgM or IgG immune complexes, but rather IgA. Additionally, HSP does not usually present with a high fever or significant organ dysfunction.
**Option B:** This option is incorrect because Kawasaki disease is a medium vessel vasculitis that typically affects children but is characterized by the deposition of IgM immune complexes and coronary artery involvement, not IgA.
**Option C:** This option is incorrect because Eosinophilic granulomatosis with polyangiitis (EGPA) is a medium vessel vasculitis that typically affects adults and is characterized by the deposition of IgG and IgM immune complexes, not IgA.
**Option D:** This option is incorrect because Goodpasture syndrome is a small vessel vasculitis that typically affects adults and is characterized by the deposition of IgG antibodies against the basement membrane, not IgA.

**Clinical Pearl / High-Yield Fact**
HSP is a classic example of a small vessel vasculitis, characterized by the deposition of IgA immune complexes and neutrophilic infiltration. It is essential to recognize the clinical features of HSP to differentiate it from other vasculitides.

**Correct Answer:** C.