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, sallallahu ‘alayhi wa sallam, is His slave and Messenger.
Training the child to fast is required so that it becomes familiar to him, as we have already highlighted in fatwas 23435 and 26790, especially the child who has reached the age of ten. Ar-Rubayyi’ bint Mu‘awwith, may Allah be pleased with her, said about training their children to fast, “We made our children fast. We would make toys of wool for them, and when anyone felt hungry and wept for food, we gave them these toys to distract them till it was the time to break the fast...” [Al-Bukhaari and Muslim]
However, scholars said that the child should be trained to fast only when he is able to do so; if the child cannot bear it, then he should not be made to fast. Ibn Qudaamah wrote:
“As the child reaches the age of ten and he is physically able to observe fasting, he should be obliged to fast and should be disciplined when neglecting it in order to train him to fast just as he is trained to perform the obligatory prayers. Some of the scholars who held that the child should be ordered to fast only if he is physically able were ‘Ataa', Al-Hasan, Ibn Seereen, Az-Zuhri, Qataadah, and Ash-Shaafi‘i. Al-Awzaa‘i said that the child should fast if he is able to fast for three consecutive days without getting weak and exhausted ... and he is not obliged to fast until he reaches puberty.” [Al-Mughni - abridged]
If it is difficult for your children to fast because of the long daytime, then do not make them fast.
Allah knows best.