SB 10.4.5

bahavo hiṁsitā bhrātaḥ
 śiśavaḥ pāvakopamāḥ
tvayā daiva-nisṛṣṭena
 putrikaikā pradīyatām
bahavaḥ — many; hiṁsitāḥ — killed out of envy; bhrātaḥ — my dear brother; śiśavaḥ — small children; pāvaka-upamāḥ — all of them equal to fire in brightness and beauty; tvayā — by you; daiva-nisṛṣṭena — as spoken by destiny; putrikā — daughter; ekā — one; pradīyatām — give me as your gift.
My dear brother, by the influence of destiny you have already killed many babies, each of them as bright and beautiful as fire. But kindly spare this daughter. Give her to me as your gift.

Here we see that Devakī first focused Kaṁsa’s attention on his atrocious activities, his killing of her many sons. Then she wanted to compromise with him by saying that whatever he had done was not his fault, but was ordained by destiny. Then she appealed to him to give her the daughter as a gift. Devakī was the daughter of a kṣatriya and knew how to play the political game. In politics there are different methods of achieving success: first repression (dama), then compromise (sāma), and then asking for a gift (dāna). Devakī first adopted the policy of repression by directly attacking Kaṁsa for having cruelly, atrociously killed her babies. Then she compromised by saying that this was not his fault, and then she begged for a gift. As we learn from the history of the Mahābhārata, or “Greater India,” the wives and daughters of the ruling class, the kṣatriyas, knew the political game, but we never find that a woman was given the post of chief executive. This is in accordance with the injunctions of Manu-saṁhitā, but unfortunately Manu-saṁhitā is now being insulted, and the Āryans, the members of Vedic society, cannot do anything. Such is the nature of Kali-yuga.

Nothing happens unless ordained by destiny.

tasyaiva hetoḥ prayateta kovido
 na labhyate yad bhramatām upary adhaḥ
tal labhyate duḥkhavad anyataḥ sukhaṁ
 kālena sarvatra gabhīra-raṁhasā

(Bhāg. 1.5.18)

Devakī knew very well that because the killing of her many children had been ordained by destiny, Kaṁsa was not to be blamed. There was no need to give good instructions to Kaṁsa. Upadeśo hi murkhāṇāṁ prakopāya na śāntaye (Cāṇakya Paṇḍita). If a foolish person is given good instructions, he becomes more and more angry. Moreover, a cruel person is more dangerous than a snake. A snake and a cruel person are both cruel, but a cruel person is more dangerous because although a snake can be charmed by mantras or subdued by herbs, a cruel person cannot be subdued by any means. Such was the nature of Kaṁsa.