Mazel is changed by G-d

 Ohr HaChaim (Vayikra 26:12) And I will turn to you, etc." This is related to our Sages saying That Jews are not determined by Mazel. G-d uproots this mazel from one place and placed it in another place. So even though children life and livelihood are said to be controlled by mazel and not merit. G-d changes the Mazel This is why G-d had to say: "I will turn to you" before mentioning that He would make the Jewish people fruitful. The word “I will turn” is indicative of G-d personally involving Himself in the fertility of the Jewish people instead of leaving the matter in the hands of the agent He has appointed as part of the laws of nature to deal with such tasks. It is also possible that when the verse continues with "I will multiply you," that this refers to a second key G-'d holds in His hands, i.e. the key to livelihood. Adequate food assists physical growth. The word  I will establish then refers to the third key G-d holds in His hands, the key to life and death. The word I will turn may thus be understood as G'd granting us access to all the three keys in His possession.