Fulfilling promises given to a disabled child
12-4-2017 | IslamWeb
Question:
Assalaamu alaykum. Is it permissible for an average human being to not fulfill their word to a cognitively or physically disabled child? A disabled child told an individual that they would like them to always keep informing them on how they should behave apporiately if they caught them doing otherwise. This individual agreed, but the disabled child has an issue of not listening to others (one of their defects that Allaah created within them). The individual made some conditions for the disabled child to adhere. The disabled child told the individual that they will fulfill them, but the disabled child broke those conditions on multiple occasions. It came to the point that the disabled child fully understood the conditions and was trying their best to follow them. However, the individual did not fulfill their one condition that the disabled child had asked them for. The individual stopped informing them about their behavior, and now the disabled child is in tears.
Answer:
All perfect praise be to Allah, The Lord of the worlds. I testify that there is none worthy of worship except Allah and that Muhammad 
is His slave and Messenger.
Fulfilling the promise is recommended according to the view of the majority of the jurists, but it is not obligatory. We have already explained this in fatwa 86010.
So one should fulfill the promise as much as possible; fulfilling it is one of the good traits of Islam and its good moral characters.
If that person is disabled, then perhaps he did not mean guidance in itself and complying with the directives that he is given; rather, he intended to satisfy a psychological need, which is his need for people’s sympathy and compassion. So it is more appropriate to be patient with him and seek the reward from Allah.
Allah says (what means): {…and do good - that you may succeed.} [Quran 22:77]
Allah says (what means): {And do good; indeed, Allah loves the doers of good.} [Quran 2:195]
Abu Hurayrah 
narrated that the Prophet said, “Whoever removes one of the difficulties of this world from a believer, Allah will remove one of his troubles on the Day of Resurrection; the one who finds relief for a hard-pressed person, Allah will make things easy for him on the Day of Resurrection; the one who conceals the faults and sins of a fellow Muslim, Allah will conceal his own faults and sins in this world and in the Hereafter; and Allah supports His slave as long as the slave is supportive of his brother.” [Al-Bukhaari and Muslim]
Besides, Ibn ‘Umar narrated that the Prophet said, “The most beloved deed to Allah is to bring joy to a Muslim.” [Al-Tabaraani]
Allah knows best.