The Children of Llullaillaco, also known as the Mummies of Llullaillaco, are three Inca child mummies discovered on 16 March 1999 by Johan Reinhard and his archaeological team near the summit of Llullaillaco, 6,739 meters (22,110 ft) stratovolcano in the Andes mountains on the border between Chile and Argentina. The children were sacrificed in an Inca religious ritual that is believed to have taken place c. 1500. In this ritual, the three children were drugged, then placed inside a small chamber 1.5 meters (4.9 ft) beneath the ground, where they were left to die. According to Reinhard, the mummies "appear to be the best-preserved Inca mummies ever found", and other archaeologists have expressed the same opinion, calling them among the best-preserved mummies in the world.

On 20 June 2001, Argentina's National Commission of Museums, Monuments, and Historic Places declared the Children of Llullaillaco to be National Historic Property of Argentina. Since 2007, the mummies have been on exhibition in the Museum of High Altitude Archaeology in the Argentine city of Salta.

The mummies have been the subject of controversy and the display of the bodies is opposed by  indigenous people.

Rogelio Guanuco, the leader of the Indigenous Association of Argentina (AIRA), called the display "a violation of our loved ones", saying that "Llullaillaco continues to be sacred for us. They should never have profaned that sanctuary, and they should not put our children on exhibition as if in a circus." Fermín Tolaba, chief of the Lules, said that the mummies "should have stayed in their territory", and that "now that [the mummies] are already exhumed, [the museum] would have to return them. It is not good that the museum is earning money with that, charging an admission for something that doesn’t belong to it."

Child sacrifice, referred to as capacocha or qhapaq hucha, was an important part of the Inca religion and was often used to commemorate important events, such as the death of a Sapa Inca. Human sacrifice was also used as offering to the gods(!) in times of famine, and as a way of asking for protection. Sacrifice could only occur with the direct approval of the Inca emperor. Children were chosen from all over the sprawling Inca empire, and were picked primarily based on their "physical perfection". Children chosen for sacrifice were generally "sons and daughters of nobles and local rulers". They were then taken hundreds or thousands of miles to Cusco, the capital, where they were the subject of important purification rituals. From there, the children were sent to high mountaintops throughout the empire to be sacrificed. According to traditional Inca belief, children who are sacrificed do not truly die, but instead watch over the land from their mountaintop perches, alongside their ancestors. The Inca considered it a great honor to die as a sacrifice.

Llullaillaco is a stratovolcano of 6,739 metres (22,110 ft), in the Andes mountains on the border between Chili and Argentina. The burial site was covered by five feet of earth and rock at the time of discovery. The site where the mummies were found has been described as "the world's highest archaeological site".

Llullaillaco is in the Atacama Desert, the driest non-polar desert on Earth. The extreme dryness of the air is a major reason for the excellent preservation of the mummies for 500 years. Dryness and cold temperatures are both known to significantly reduce the decomposition rate of human remains, and the extreme environmental conditions at the summit of Llullaillaco are therefore very conducive to preservation.

In 1999, Johan Reinhard and his team of researchers set out into the high Andes to search for Inca ritual sacrifice sites. Three days into their search, Reinhard's team discovered a grave site containing three mummified children: two girls and one boy. Several gold, shell and silver statues, textiles and pottery were also found. The younger girl's body had been struck by lightning after her death, causing burn damage on her body, especially her face and shoulder. The other two mummies were not affected. Statues made of precious metals and textiles were among the many goods found in the graves.

Several times, the expedition came close to failure. After a long acclimatization process, including a month spent exploring a lower-elevation mountain nearby, the team finally approached close to the summit of Llullaillaco after establishing a series of camps throughout the ascent. Throughout this expedition, the researchers braved severe winds over 70 miles per hour (31 m/s), and extreme temperatures, at one point reaching −40 °C (−40 °F). Furthermore, at their final camp, at an elevation of 6,600 meters (21,700 ft), a storm broke and lasted for four days. According to Reinhard, the team "[was] about to give up" when they spotted an artificial layer in the site that indicated they should continue the investigation. The researchers followed the artificial layer, which eventually led them to the burial of one of the mummies.

Three mummies were found at the Llullaillaco burial site: la doncella (the maiden), la niña del rayo (the lightning girl), and el niño (the boy). Once at the top of the mountain, they were allowed to fall asleep, and then placed in a small tomb 1.5 meters (4.9 ft) underground, where they were left to die. Additionally, they were fed a high-protein diet before they were sacrificed.

The mummies were in exceptional condition when found. Reinhard said that the mummies "appear to be the best-preserved Inca mummies ever found", additionally saying that the arms were perfectly preserved, even down to the individual hairs. The internal organs were still intact, and one of the hearts still contained frozen blood. Because the mummies froze before dehydration could occur, the desiccation and shriveling of the organs that is typical to exposed human remains never took place.

The oldest mummy, a girl found to be around the age of fifteen, was dubbed la doncella.

She has become widely known as the "Maiden of Llullaillaco". A bacterial infection was discovered in her lungs during an examination. She wore a dress with her hair elaborately braided, along with a feather-adorned headdress. DNA testing indicated that the two girls were half-sisters, while the boy was not related. She died in her sleep, a fate shared with the other children.

It is believed that La Doncella was an aclla, or Sun Virgin – she was a virgin, chosen and sanctified at around the age of ten years old, to live with other girls and women who would become royal wives, priestesses, and sacrifices. The practice of ritual sacrifice in Inca society was intended to ensure health, rich harvests and favorable weather.

La niña del rayo was approximately six years old when she was sacrificed

La niña del rayo's face, one of her ears, and part of her shoulder were damaged by a lightning strike that occurred after her death. Her head was lifted high, and she was facing toward the south-west. She was wearing a traditional light brown acsu dress, and her head, along with part of her body, was wrapped in a thick wool blanket. Additionally, her entire body was wrapped in another blanket, this one an embroidered blanket of red and yellow. Her skull appears to have been intentionally elongated.

La niña del rayo appears to have been treated less roughly than el niño, but without the care with which la doncella was treated.

The el niño was about seven years old when he was sacrificed

The body of el niño had been tightly wrapped, as some of his ribs and pelvis were dislocated. He apparently died under stress, as vomit and blood were found on his clothing. There also appeared to be an infestation of nits in his hair. He was the only child to be tied up. Lying in the fetal position, he was wearing a gray tunic, a silver bracelet, and leather shoes, and had been wrapped in a red and brown blanket. The skull of el niño had been slightly elongated, similarly to that of la niña del rayo. Due to the way in which he was tied up, it is believed that he may have died of suffocation.

El niño was buried with a collection of small objects, some of them depicting finely dressed men driving caravans of llamas, and others depicting a ritual activity in which men use slingshots to launch cannons into the lagoons at the end of the dry season to hasten the coming of the rains.

The children were drugged before the start of the sacrificial ritual

According to a biochemical analysis of la doncella's hair, the children were drugged with alcohol and coca before the start of the sacrificial ritual. La Doncella had been drugged by leaves and a maize beer known as chica. Though all three of the sacrifices consumed significant amounts of these substances prior to the ritual, a hair sample analysis shows that la doncella consumed significantly more coca and alcohol than either el niño or la niña del rayo. Her hair contained the highest concentration of coca ever found in Andean human remains.

The high Andes region from which the mummies were taken is believed to be home to at least 40 other similar ritual burial sites. However, in order to "have good relations with the Indian people", no more mummies will be removed from the area, according to Gabriel Miremont, the designer and director of the Museum of High Altitude Archaeology, which hosts the exhibit displaying the mummies. Other indigenous people supported the research, however. The Third World Congress of the Quechua Language in late 2004 brought together 300 representatives from Andean countries, at its conclusion the congress passed a resolution "The congress approves supporting investigations of the :Llullaillaco Children (Salta, Argentina) and the diffusion of such investigations for recognizing the greatness and the evolution of our ancestors from their origins to the present day." (ILKHA)