It happened along the 2100 block of South Alden Street in the city's Kingsessing section.
Police said just after 5 p.m., a 4-year-old boy picked up his father's gun that was left in a bedroom on a bed and shot himself in the right leg.
Officials said the father quickly rushed the boy to Children's Hospital of Philadelphia, where he is listed in stable condition.
No charges or arrests have been made.
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