Clairton fire Chief John Lattanzi said it appeared the three perished from smoke inhalation, likely before the first responders appeared on the scene.
Two Clairton police officers, Tim Huschak and Keith Zenkovich, were the first to arrive at the home, Chief Lattanzi said.
Firefighters arrived within minutes, Chief Lattanzi said.
The heat was too intense for them as well, and they worked instead on knocking down the flames.
With four fire companies from Clairton
and nearby communities, and a fifth company on standby for emergency extractions, the blaze quickly was contained.
It did not spread to the adjoining units in the row, nor did it travel along the common roof of the structure.
Two of the victims were found in a rear bedroom, the third child in a front bedroom, Chief Lattanzi said.
The children were taken to Jefferson Hospital
, where they were pronounced dead.
Officials are investigating the cause of the fire, but Chief Lattanzi said it appears to have started in the first-floor kitchen.