**Core Concept**
The patient's presentation of generalized swelling, proteinuria, and the presence of hyaline and fatty casts is indicative of nephrotic syndrome, a clinical condition characterized by massive proteinuria (>3.5 g/24h), hypoalbuminemia, and edema.

**Why the Correct Answer is Right**
Nephrotic syndrome is typically caused by damage to the glomerular filtration barrier, leading to the loss of large amounts of albumin in the urine. The presence of hyaline and fatty casts in the urine is a result of the breakdown of proteins in the tubules. The absence of hematuria rules out nephritic syndrome, which is characterized by inflammation of the glomeruli and hematuria. In this patient, the likely cause of nephrotic syndrome is minimal change disease, a common cause of nephrotic syndrome in children.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because nephritic syndrome is characterized by inflammation of the glomeruli, hematuria, and hypertension, which are not present in this patient.

**Option B:** This option is incorrect because membranous nephropathy is a common cause of nephrotic syndrome in adults, not children.

**Option C:** This option is incorrect because focal segmental glomerulosclerosis (FSGS) is a cause of nephrotic syndrome in children, but it is not the most likely diagnosis in this case, given the patient's age and the absence of other symptoms.

**Clinical Pearl / High-Yield Fact**
Hyaline and fatty casts are a hallmark of nephrotic syndrome, and their presence in the urine can help differentiate it from nephritic syndrome.

**Correct Answer:** C.