The shooting happened just before 9 p.m. at Academy Park High School on the 300 block of Calcon Hook Road in Delaware County.
A game between Academy Park and Pennsbury High School had just ended when the gunfire erupted near the concession stand.
Action News spoke with the girl's family, who identified her as Fanta Bility.
"My daughter was a nice person. She was so kind," said Tennah Kromah, Fanta's mother.
Kromah is now planning for Fanta's funeral instead of her future.
She took a picture of Fanta at Friday's football game, sitting in the stands, before the shooting that claimed her life.
"They were shooting. Everybody was running," said Kromah.
Kromah says she was also shot but is expected to be okay.
"She just got caught in somebody's terrible act, and she became the victim," said Abu Bility, Fanta's uncle.
He adds this kind of thing in the community is very scary and feels nobody is safe anywhere.
"If you take your kids on the school property, I think you expect them to be safe," he said.
The family says Fanta died at Mercy Fitzgerald Hospital in Lansdowne, Delaware County, from a gunshot wound to the chest.
Two other juveniles were also wounded. No details were immediately available about those victims.
Action News has learned three people are in custody, and weapons have been recovered.
A witness on the scene was standing right next to the little girl who was shot.
"When she got shot she went down, grabbed my leg as she was going down," witness Deanna Bankston said. "I kneeled down but then her mom kneeled down next to her, and then I had to get up and go look for my children."
"The bullets burnt my one of my ears going by," Bankston continued. "The sounds the bullets make going past your ear is crazy. I'm just glad all my kids made it."
WBCB radio was just wrapping up its broadcast of the game when the shooting happened. The sound of the gunshots could be heard on air.
"It was Academy Park 42 and Pennsbury nothing," the announcer is heard to say just before a barrage of gunshots.
Meanwhile, viewer video sent to Action News from the moments after the shooting showed people, including football players, lying on the field as police vehicles with lights and sirens begin arriving on the scene.
Some 100 to 200 people were leaving the game as the shots rang out.