UPDATE 4:50 p.m.:
Police have announced that at 1:55 p.m. today, 2-month-old Hassan Armstrong succumbed to injuries to his ribs and skull sustained on Friday afternoon.
Armstrong's father Brian Armstrong was arrested for the beating and remains in police custody.
Police have charged a father with severely beating his 2-month-old son, leaving the child in critical condition.
Brian Armstrong, 20, is charged with aggravated assault for the incident, police said.
Police were called at 4:20 p.m. on Friday by Einstein Hospital staff, who had a 2-month-old baby in the emergency room in critical condition.
The baby was transported to St. Christopher's Hospital for Children and is in critical condition as of Sunday morning, police said.
The Philadelphia Police Department's Homicide Unit is investigating the case and has charged Armstrong, of 6200 Old York Road.