The 2-year-old's mother was among the victims, Philadelphia Police Chief Danielle Outlaw told a news conference. The most seriously wounded victim was a teen listed in critical condition, she added.
The gunfire erupted shortly before 6 p.m. local time (2300 GMT) just a few hundred feet away from an elementary school, but Outlaw said the incident did not appear to have started there.
"As a parent myself I understand the fear that people have," Outlaw said.