It happened around 10 p.m. on June 24 on the 2600 block of Aramingo Avenue.
Police say the two victims, a 15-year-old and 12-year-old, were playing basketball at the Cione Recreation Center.
That's when an unknown male started arguing with them.
The confrontation was caught on surveillance cameras.
The unknown male called over a second suspect, along with three to five additional males, and assaulted one of the victims.
The suspects stole an iPhone and a wallet containing $100.
One of the teens suffered minor bruising to his back and side from being kicked and punched, police say.
Anyone with information should call police at 215-686-3243/3244.