Hamsa, Suvikrama, Kratha, Damana, Ripumardhana, Krodhahantha.
The six sons of the demon Kalanemi, devotees of Vishnu.
They asked Brahma for the favor of not to be killed by any being.
So they turned the demon Hiranyakashipu against them. He cursed them, that one day they would be killed by their father. They were born to Vasudeva and Devaki.
Kalanemi, who was born as Kamsa, received the prophecy that the eighth child of the two would be his executor.
He asked Vasudeva to kill his children. Vasudeva carried out the curse of Hiranyakashipu by killing his first six sons. The seventh (Balarama) and eighth child (Krishna) were saved.
To read the story visit
http://hindumythologyforgennext.blogspot.com/2014/04/krishna-dark-lord-of-dwaraka-prelude.html
http://hindumythologyforgennext.blogspot.com/2017/07/little-krishna-part-1.html
http://sushmajee.com/mahaabhaarat/krishn/index-krishn.htm