To my knowledge, the first six sons of Mata Devaki were the grandsons of the Asura Hiranyakashipu, the sons of Kalanemi. It is said that they rejected his affection for Tapasya to Brahma, and so were cursed by their grandfather:
ShaDgarbhANAM varaM datvA svayaMbhUstridivaM gataH |
tato hiraNyakashipuH saroSho vAkyamabravIt ||2-2-20- Vishnu Parva, Harivamsa
After granting the boon to ShaDgarbhA, the self-born brahmA returned to his heavenly abode. Then hiraNyakashipu angrily spoke these words:
mAmutsR^ijya varo yasmAdvR^ito vaH padmasaMbhavAt |
tasmAdvastyAjitaH snehaH shatrubhUtAMstyajAmyaham ||2-2-21
Abandoning me, you have received boons from brahmA. Hence you have rejected my affection. I am rejecting you, who have become my enemies.
ShaDgarbhA iti yo.ayaM vaH shabdaH pitrAbhivardhitaH |
sa eva vo garbhagatAnpitA sarvAnvadhiShyati ||2-2-22
The same father who called you ShaDgarbhA and brought you up, will kill all of you when you are conceived.
ShaDeva devakIgarbhAH shaDgarbhA vai mahAsurAH |
bhaviShyatha tataH kaMso garbhasthAnvo vadhiShyati ||2-2-23
All six of you, great asura-s ShaDgarbhA will become devakI's conceptions. Then kaMsa, (incarnation of your father kAlanemi) will kill you at conception.
As Kamsa is Kalanemi, and the curse was so, Kamsa had to kill all six. The seventh of course, is Balarama Dau, who was taken from Mata Devaki's womb and transferred to Mata Rohini's.
Edited by SriMaatangi - 1 years ago