BUENOS AIRES—In a working-class neighborhood of dirt streets and broken sidewalks, Pablo Martínez donned the white-and-blue jersey of Argentina’s national team to grill chicken at a soup kitchen he helps run for families struggling amid a punishing economic crisis. With galloping inflation and economic stagnation pushing 43% of the population into poverty, the number of hungry children showing up to his cafeteria on the outskirts of the capital has been rising, Mr. Martinez said. The daily hardship he and his neighbors face in a poor barrio is leaving an indelible impact.

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