Huaman said the high salt content of the sand in the area likely caused a natural mummification of the youngster, whose gender has not been determined.
Bits of skin remained on the arms and legs, while hair was found on the head, which was separated from the body.
There were also remains of teeth in the jaw.
"The find is very important because it is so well preserved," said Huaman, who leads a team of archaeologists from the University of San Marcos, in Lima.
Next to the mummy the team found a stone weapon, a plate, a copper needle, and remains of textile, corn and chili.
In February 2022, archaeologists found 20 mummies, including eight of children, at Cajamarquilla.
