Ego's Children

Ego's children were the children of the Celestial Ego

Guardians of the Galaxy Vol. 2
For the past centuries, Ego has affairs with many women and has many children. The children are abducted from their homes by Yondu Udonta and given to their father. However, none of them inherit Ego's celestial genes, leading him to kill those who were a disappointment. He later buries them below in the caverns of his planet. One day, he crashlands on Earth and meets a woman named Meredith Quill. While Meredith Quill was in early pregnancy with Peter, Ego and Meredith drive down a road while Meredith sings to "Brandy (You're A Fine Girl)". Ego shows Meredith a plant he had implanted in the soil, and says it will one day "be across the universe". Not knowing what he's talking about, Meredith says she likes the way he said it. Just as they kiss, the plant within the earth begins to grow. Shortly after Peter is born, Ego abandons Meredith and their newborn son. (Guardians of the Galaxy Vol. 2

Ego later instructs Yondu to abduct his son, Peter, from Earth. However, Yondu learns Ego has been killing the kids Yondu collected for the Celestial. To spare another child of the same fate, Yondu keeps Peter and raises him after his mother, Meredith Quill's, death.

Mantis also gets to know several of the kids.

Discovery
After Gamora and Nebula walk away from their crashed M-ship, Gamora spots a cavern and both sisters enter, only to find the mutilated bodies of many other children. Both women are horrified to see what they find. Nebula says that they both need to get the hell off the planet.

Later, Gamora confronts Mantis, who later reveals that the bodies in the caverns are Ego's Children and they all realize Peter is in danger.