In young children, especially under 5 years, **vesicoureteral reflux (VUR)** is the most common cause of chronic pyelonephritis, leading to renal scarring. VUR allows urine to flow backward from the bladder to the kidneys, causing repeated infections and progressive kidney damage. While tuberculosis and interstitial nephritis can cause renal issues, they are less common in this age group. Trauma is rare in 3-year-olds. Pyelonephritis from VUR is a leading cause of renal scarring in early childhood.

**✓ Correct: C. Vesicoureteral reflux induced pyelonephritis**