You can spot them prowling the streets of Mexico City's wealthy enclaves in sports cars. The guys wear their hair slicked back and designer shirts with the top three buttons open. The women have expensive bags and sunglasses. They are nearly always followed by a black SUV packed with armed bodyguards.

They are known in Mexico as "Juniors"—the sons and daughters of the country's elite, young people whose love of brand names is surpassed only by their sense of entitlement. Juniors grow up to dominate the upper echelons...