Nelly Murillo, 18, and her son Yudier Moreno, not yet one-years old, were near the site where the Cessna 303 crashed on Saturday in thick brush.
"It's a miracle. It is a very wild area and it was a catastrophic accident," Colonel Hector Carrascal, commander of the Colombian Air Force in Antioquia department, told AFP.
"His mother's spirit must have given him strength to survive."
Murillo and her baby were taken by helicopter to a nearby hospital with minor injuries, said Carrascal, adding that he was stunned they were alive.
"The lady has wounds and minor burns and apparently the child is unharmed," the Colombian Air Force said in a statement.
The plane's pilot, Captain Carlos Mario Ceballos, died in the crash and rescuers found his body in the aircraft.
They discovered the doors of the plane ajar and suspected that survivors may have clambered out.
A 14-person search-and-rescue team scoured the dense forest for several days before finding the mother and child.
The plane was travelling between Nuqui and Quibdo in northwest Colombia when it crashed.
Investigators were looking at the cause.