Who is the "heir (wārith)" referred to here?

Imām Ibn al-Jawzī (d. 597/1201) summarized the scholars' opinions in his book "Zād al-Masīr" as follows:

1. It refers to the heir of the child. [ʿAṭāʾ, Mujāhid, Saʿīd ibn Jubayr, Ibn Abī Laylā, Qatādah, al-Suddī, al-Ḥasan ibn Ṣāliḥ, and Muqātil, among others]. Among those who hold this opinion, there are different interpretations: (i) Some say it is the heir of the child from among his agnates (male relatives through the father's side), whoever they may be. This is reported from ʿUmar, ʿAṭāʾ, al-Ḥasan, Mujāhid, Ibrāhīm, and Sufyān. (ii) Others say it is the child's heir, whether male or female. This is reported from Ibn Abī Laylā, Qatādah, al-Ḥasan ibn Ṣāliḥ, Isḥāq, and Aḥmad ibn Ḥanbal. (iii) Another group states it is anyone who is a blood relative forbidden for marriage among the child’s heirs. This is reported from Abū Ḥanīfah, Abū Yūsuf, and Muḥammad.

1. It refers to the heir of the father. [Reported from al-Ḥasan and al-Suddī]
2. It refers to the surviving parent of the child after the death of the other. [Reported from Sufyān]
3. It means the child himself, and the obligation of maintenance falls upon him; if he possesses nothing, then it is upon his agnates (male relatives through the father's side). [Al-Ḍaḥḥāk, Qabīṣah ibn Dhuʾayb] ʿAlī ibn ʿUbayd Allāh, commented: "This last opinion does not contradict the view that 'the heir' refers to the heir of the child, because the obligation of maintenance rests upon the heir if the one requiring support is in financial difficulty."