Police say a man was taken into custody on Thursday, but he has not been formally charged.
Sources say the suspect was arrested as he showed up in court on unrelated charges.
Yaseem Munir Jenkins was shot four times, including once in the head, while inside a vehicle in the city's Hunting Park section.
A family spokesperson released this statement to Action News on behalf of Yaseem's mother:
"My son is fighting for his life and it is not fair. He's innocent, so precious, and his smile will brighten up anyone's day. He's such a bubbly kid. So loving and lovable. How could anyone be so heartless! Please do the right thing and help us find some form of closure or answers in this tragic situation. Help us find the shooter. I can't eat or sleep. I need justice for my baby...For the coward who did this to him, you will pay, even if it not today or tomorrow. God will handle you accordingly."
Yaseem's shooting happened less than 24 hours before another shooting that left a 2-year-old girl dead, her mother and another man injured. Two suspects are now in custody in that case.
Yaseem continues to fight for his life at Children's Hospital of Philadelphia.
"Please continue to keep my baby in your prayers and mention him by name for he is not just an 11 month old, he's my world. Thank you," the family added.