**Core Concept**
The child's presentation of hematuria, fragmented red blood cells (RBCs), thrombocytopenia, and bilateral kidney enlargement after a diarrheal illness suggests a post-infectious glomerulonephritis (PIGN) with a possible diagnosis of post-streptococcal glomerulonephritis (PSGN).

**Why the Correct Answer is Right**
Post-streptococcal glomerulonephritis is a common cause of PIGN, particularly in children. It occurs after a streptococcal infection, often a skin or throat infection, which triggers an immune response leading to the formation of immune complexes that deposit in the glomeruli, causing inflammation and damage. The fragmented RBCs (schistocytes) in the blood film are indicative of microangiopathic hemolytic anemia, a common finding in PSGN. Thrombocytopenia is also seen due to the consumption of platelets in the process of microangiopathic hemolytic anemia.

**Why Each Wrong Option is Incorrect**
* **Option A:** Henoch-Schönlein purpura (HSP) is a form of vasculitis that affects small blood vessels and is characterized by the deposition of IgA immune complexes. While it can cause kidney involvement, the presence of fragmented RBCs and thrombocytopenia is less typical.
* **Option B:** Minimal change disease is a primary glomerulopathy that typically presents with nephrotic syndrome in children, but it is not associated with hematuria, thrombocytopenia, or microangiopathic hemolytic anemia.
* **Option C:** Acute tubular necrosis (ATN) is a form of acute kidney injury that can occur after a diarrheal illness, but it is not typically associated with fragmented RBCs, thrombocytopenia, or bilateral kidney enlargement.

**Clinical Pearl / High-Yield Fact**
The triad of hematuria, thrombocytopenia, and fragmented RBCs (schistocytes) in a child with a recent diarrheal illness should raise suspicion for post-streptococcal glomerulonephritis.

**Correct Answer: C. Acute Tubular Necrosis**