Final answer:
Wilms tumor is a malignant tumor of the kidney that primarily occurs in children, distinguishing it from other kidney-related issues such as benign tumors or kidney stones.
Step-by-step explanation:
Wilms tumor is a malignant tumor of the kidney, usually occurring in children. This type of cancer is one of the kidney tumors that can affect pediatric patients. Wilms tumor, unlike some other types of kidney disorders such as kidney stones or polycystic kidney disease (PKD), is specifically a malignancy that can have serious implications if not treated. It's different from common benign tumors or other renal conditions such as nonmalignant tumors related to kidney stones, hydronephrosis, or congenital abnormalities of the urinary tract.
The correct answer to the student's question is: 1) malignant tumor of the kidney, usually occurring in children.