Police said Hezekiah Robinson fell Tuesday through an opening in a window where an air conditioner had been removed, the Philadelphia Daily News reported Wednesday.
The boy had climbed onto a bureau drawer left open in a back bedroom in an apparent attempt to look out the window, police said. He fell out of the window to the concrete below.
He was pronounced dead about 2 1/2 hours later at a hospital.
The boy's mother, Lonnia Robinson, 22, his aunt and a cousin, 3, were in the apartment at the time, police said.
No charges had been filed.