Q. My young child insists on fasting in Ramaḍān even though it harms him due to his young age and the weakness of his health. So, should I be harsh in making him stop?
A. When a person is young and has not reached the maturity stage then fasting is not compulsory on them. But, if the young person can fast without difficulty then they are to be commanded [to fast]. The Companions used to make their children fast (Bukhārī, 1960, Muslim, 1136 & others) even to the extent that the children would cry, in which case the Companions would offer them toys to be distracted. Yet, if it is certain that this fasting will harm the child then they must be prevented. For if Allah has prevented us from giving children their money out of fear that they will use it for corruption, then preventing what might harm their bodies is even more emphasised. That said, the prevention should not be harsh, as this is not the way of educating children.
Shaykh Ibn ʿUthaymīn – Fiqh al-ʿIbādāt (p. 225)