Allah said:

(No mother shall be treated unfairly on account of her child,) meaning, the mother should not decline to rear her child to harm its father. The mother does not have the right to refrain from suckling the child after giving birth, unless she suckles him/her the milk that is necessary for his/her survival. Later on, she is allowed to give up custody of the child as long as she does not do that intending to harm the father. In addition, the father is not allowed to take the child from his mother to harm the mother. This is why Allah said:

(...nor father on account of his child.) meaning, by taking the child from its mother intending to harm the mother. This is the Tafsir of Mujahid, Qatadah, Ad-Dahhak, Az-Zuhri, As-Suddi, Ath-Thawri and Ibn Zayd, and others on this Ayah.

Allah then said:

(And on the (father's) heir is incumbent the like of that (which was incumbent on the father).) meaning, by refraining from harming the relative (of the father, i.e., his infant), as Mujahid, Ash-Sha`bi and Ad-Dahhak stated. It was also reported that (the Ayah requires) the inheritor (of the father) to spend on the mother of the child, just as the father was spending, and to preserve her rights and refrain from harming her, according to the Tafsir of the majority of the scholars. We should state that Ibn Jarir has explained this subject in detail in his Tafsir and that he also stated that suckling the child after the second year might harm the child's body and mind. Sufyan Ath-Thawri narrated that `Alqamah asked a woman who was suckling her child after the second year ended, not to do that.