Teaching children the glorious Qur’an and the Islamic principles is the responsibility of their parents from an early age which is the best period for implanting Islamic ethics. However, applying that should be according to the abilities of the children which differ from one child to another; and hence, different methods of teaching are required.
In his response to your question, Sheikh Muhammad ibn Adam Al-Kawthari, a teacher of various traditional Islamic sciences at Jami`at `Ulum Al-Qur’an in Leicester, says:
Parents are responsible for the religious and secular education of their children. Children should be taught the book of Allah, both its method of recitation and the actual implementation of the injunctions contained therein. They should also be taught the disciplines of life, the basics of Islamic doctrine that includes `aqeedah, Oneness of Allah and His attributes, seerah of the blessed Messenger of Allah (peace and blessings of Allah be upon him), basics of what is lawful and what is unlawful, and fiqh with regards to salah, fasting, and so on.
From an Islamic perspective, there is no fixed age before or after which parents may or may not teach children the Qur’an or any other aspect of Islamic knowledge. As such, a child may differ from another in his mental capability and intellectual capacity. Some children are seen to mature before others. At times, it is observed that a child is similar to another in age, but the difference in their understandings is huge.
therefore, this will be a decision that is made by the parents of the child. If a child shows signs of excellence and has a great memory, it would be wise to begin teaching him the Qur’an even at an early age. This is especially so, as memorization is very effective at a young age. There have been incidents in Islamic history, where a child is born having memorized many parts of the Qur’an due to the fact that the mother had been regularly reciting the Qur’an during pregnancy.
however, if this will have a negative affect on the child, then parents should start teaching him/her later on when he has grown slightly older. Some children may be good at grasping other things, such as good habits, the ability to do domestic work, and so on, rather than memorization. For them, it would be wise to learn about social conduct and behavior, rather than the more foundational aspects of knowledge.
however, it is generally observed, that memorization is most effective when carried out at a young age. There are many examples where children as young as seven have memorized the Qur’an and that it did not have a harmful effect on them in any way. I my self (not boasting, may Allah save me, but merely giving an example of personal experience) began memorizing the Qur’an at the age of seven and with the grace of Allah Almighty, I finished it at the age of nine, and I do not for one moment regret having done so. Memorization at such an age becomes firm so that even if one is neglectful of revision, it does not become lost so easily.
May Allah inspire the children of this Ummah towards learning, practicing and preaching the knowledge of Islam, and becoming a source of guidance for all humanity!