Q: From what age must a child keep the fast of Ramadaan? Boy and girl?
A: Salaah is encouraged from the age of seven. Similarly, a child can be encouraged from seven to fast, even if it is half a day. Gradually it can be increased. Only encourage the child if the health permits. By ten they should be more regular and by twelve they should be fasting fully. Once Baaligh (mature in Islamic terms), it will be Fardh.
Allah Ta’aala knows best.
Moulana Yusuf Laher