Scientists have discovered the remains of two children buried more than 11,000 years ago at a site in Alaska, providing insight into the burial practices of early society.

The Ice Age infants are the oldest human remains ever found in northern North America, according to the Business Standard.

Ben Potter, researcher at the University of Alaska in Fairbanks, said the burials and cremations are indicative of “complex behavior related to death” among North America’s first residents.

The remains were found with burial offerings and clues on what time of year they died, which could later be extrapolated into findings about the way the culture was structured. It also provides insight into how the youngest of humans were treated in ancient societies and what these societies had to do to survive — and, ultimately, their views on death.

Researchers also uncovered shaped stone points, antler foreshafts, and other primitive weapons at the site. Since they were found around the grave, it suggests to scientists that hunting was such an important part of the society that it was included in burial ceremonies.

Scientists believe the infants died in the summer, indicating that the mortality rate was high in such societies as that should have been a time of an abundance of food.

Specifically, the remains were found in Upward Sun River, a known central Alaska archaeological site. Researchers found skeletons under the cremated remains of a 3-year-old child who was discovered four years ago.

The two infants are likely both girls. Researchers have worked with local Native American tribes to treat the burial sites with respect.

After making the initial find in 2010, according to LiveScience, researchers returned to the site last year to dig even deeper, where they found the double infant burial, about 15.7 inches below the first cremated child.

At that point, the team stopped their excavation and reached out to local native groups and state officials to ask for permission to conduct further studies.

They were found with their legs bent toward their chest, and an analysis of their bones suggests that one was a late-term fetus and the other was five weeks old.

Researchers published their findings in the Proceedings of the National Academy of Scientists.