The shooting happened during what officers are calling an illegal block party along the 4600 block of 12th Street on Saturday.
Witnesses say someone started shooting into the crowd.
The 2-year-old girl, who was caught in the crossfire, was hit in the stomach.
Two other people were also shot.
Investigators say of the 200 people who were at the party during the shooting, no one has come forward with information.
"We'd like to get this person off the street because anybody who pulls out a gun, with that large amount of people out there, and an innocent child is hit like that, they have no regard for anybody else's life," said Capt. Winton Singletary of the Philadelphia Police.
The little girl is in critical but stable condition at Saint Christopher's Hospital for Children. She's expected to survive.