All perfect praise be to Allah, The Lord of The Worlds, and may His peace and blessings be upon our Prophet Mohammad and upon all his family and companions.
The rulings of Sharia apply only on the sane Muslim who has reached puberty since The Messenger of Allah (PBUH) said,"There are three (persons) whose actions are not recorded: a sleeper till he awakes, an idiot till he is restored to reason, and a boy till he reaches puberty"{Related by Abu Dawud}. Therefore, a child`s fast during the daytime of Ramadan isn`t obligatory. Rather, it is desirable since the idea isto train him/her to fast on gradual basis. Thus, once he/she grows up and reaches puberty, he/she becomes more inclined to come closer to Almighty Allah and seek recompense from Him.
Actually, this is the responsibility of the parents. They should train their children to fast through using different incentives, such as material rewards and mental support. They have to make them embrace the especial sentiments associated with this blessed month so that it becomes closer to their hearts than any other month. They should realize that Allah desires ease for us, not hardship. Rather, it is our pietythat shall reach Him. They should also realize that fasting isn`t only about abstaining from food and drink. It is also about enjoying good manners, treating others kindly, shouldering responsibility, and self-education, and this is where the objective of Sharia is achieved.
Rubayyi' daughter of Mu'awwidh b. 'Afra' said that the Messenger of Allah (PBUH) sent (a person) on the morning of Ashura to the villages of Ansar around Medina (with this message):
"………….We henceforth observed fast on it (on the day of 'Ashura) and, God willing, made our children observe that. We went to the mosque and made toys out of wool for them and when anyone felt hungry and wept for food we gave them these toys till it was the time to break the fast"{Related by Bukhari& Muslim}.
Parents should make their children fast in moderation. They shouldn`t be made to fast out of fear or to avoid mockery, because this could cause their powers to break down.
In the meantime, they shouldn`t be offered different foods and drinks during the daytime of Ramadan. Rather, parents should observe the Sharia objective mentioned above. The physical build of the child, his/her age and ability to bear fast should be taken into consideration and based on this parents should either order the child to continue the fast of that day or not so as to ward off harm.
What`s important, here, is that fast shouldn`t lead the child to hardship, and so he/she starts hating it. 'Amr bin Shu'aib reported on his father's authority that his grandfather (May Allah be pleased with him) said:Messenger of Allah (PBUH) said, "Command your children to perform Salat (prayer) when they are seven years old, and beat them for (not offering) it when they are ten, and do not let (boys and girls) sleep together". [Abu Dawud]. Misunderstanding this Hadith shouldn`t lead to making children experience hardship, because comparing fast to prayer is conditioned upon ability to bear hardship and physical build.
Finally, the signs of puberty for males are becoming fifteenor having a wet dream, but having pubic hair or menses for females. And Allah knows best.