Diti asked for a son who was mor powerful than Indra.
Aditi, Indra’s mother, warned her son. Indra entered the body of Diti and divided the child into seven parts. It screamed, Diti awakened and cursed Indra, that he would never be able to live in peace. Indra revealed that his mother instigated him. Diti curses her to one day end up in prison and lose her seven children.
Aditi lost seven children in prison in her next life as Devaki. Six were the Sadagarbha whom Vasudeva killed at the behest of Kamsa. The seventh was taken from her, not killed. It was brought into Rohini’s womb and born as Balarama, Krishna’s brother. The eighth child was Krishna.
Diti’s curse on Indra meant that he was always worried about his throne. Kashyapa and Aditi asked Vishnu to be born their son. They were born again as Dasaratha and Kausalya, and Vishnu incarnated as their son Rama. Next they were born as Vasudeva and Devaki, Vishnu incarnated as their son Krishna.
For a modified version see Prisnigarbha.