The children were rescued after a blaze broke out at a property on Beambridge Road in Basildon at 15:15 BST.
A 13-year-old boy was airlifted to Royal London Hospital and a 10-year-old boy was taken to Basildon Hospital by ambulance.
Both are in a "life-threatening" condition, Essex County Fire and Rescue Service said.
The cause of the blaze is not yet known and emergency services remain at the scene.
An investigation is under way.
Two young boys are in hospital with life-threatening injuries after a house fire in Essex.