Sirhaven Williams, 36, has been charged with endangering the welfare of a child, even though police said the gun belonged to the children's uncle who lived at the home.
The shooting happened just after 3 p.m. Saturday in the 3600 block of North 18th Street.
Police said the victim's 6-year-old brother somehow got a hold of a gun and shot the 3-year-old in the forehead in a second-floor bedroom.
Investigators said they believe a 12-year-old brother was also home at the time, but there were no adults present.
The 3-year-old boy was taken to Temple University in extremely critical condition.
Neighbors were stunned to hear of the shooting.
"When I heard about it, I just broke down," said Marainda Stewart of Tioga-Nicetown.
"I'm feeling hurt and I'm feeling destroyed inside because we have to be more protective of our children, and the things we allow them to get involved with," Helen Williams of Tioga-Nicetown said,
Charlene Aiken lives next door and told Action News she was out when the shooting happened.
"So to come home to this, it's disturbing and I hope and pray that he's going to be alright," she said. "They're sweet kids. I saw them the other day, but I didn't see them today."
People who didn't know the family gathered at the end of the street, heartbroken over what happened.
Stewart added, "I feel hurt. It's just sad to hear a child got shot. It's sad."
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