Police say flames started just before 11 last night at the home in the 300 block of North Vine Street in Berwick.
Family members couldn't make it out on the ground level of the home because smoke was so thick, so they climbed to the roof.
A neighbor and police rescued them using a ladder.
People who saw the scene were terrified.
Firefighters put the flames out within about 15 minutes.
Investigators say the fire started in the chimney.
The baby was treated by emergency responders.