We should educate our children from a young age (1-7 years) just as we tell them about food, drink, and toys. That does not mean we teach them Qur’an and Hadith from their birth, but we must give them religious teaching relevant to their perception level. For instance, saying bismillah (in the name of Allah) at the time of food and al-hamdu lillah (all praise be to Allah) at the end, also, saying subhan Allah (glory be to Allah) upon seeing thunder, rain, and so on. Don’t expect a child to learn everything at one go, only what is easy to pronounce.
The aim behind all of this is to entrench Allah’s existence in their talk and in their minds. Additionally, we need them to get used to the sayings of Allah’s Prophet Muhammad (peace and blessings be upon him) in all situations, and at least complete the study and memorization of juz’ amah of the Qur’an (one thirtieth part). Children learn their first teachings from their parents, so the parents need to teach them by example, for instance, raise your voice with du`aa’ (supplication) and the remembrance of Allah Most High when the children are around so that the children copy and memorize—this is the best method for young children (1-2 years) to learn.
Try to engage them in your daily activities such as group Prayers when they are around; assign to your son the call for the Prayer and the Iqamah. When they reach an age and proficiency of Qur’an that allows them to lead a prayer, encourage them to lead the prayer (from 7 years). Encouraging them in that way will increase their confidence both personally and Islamically as they are sharing activities with adults.
Also, you will have to be prepared to answer (calmly and logically) some awkward questions. For example, when they ask you about the existence of Allah Most High and our inability to physically see him, you can reply with the following:
Ask them first if any modern appliance could have existed or been crafted without a creator. they will then reply with “No, everything like cars, televisions, and so on, must have been created by someone.” You then should say, “Okay, so some of those creators we saw and some others we did not see”, similarly, the earth, solar system, and the whole universe must have a creator, a sustainer, and a maintainer, whom we don’t see—and that is Allah Most High. You can further explain and give other examples such as the CCTV cameras, they were put there by the police to patrol the streets and public places but that does not mean that they were put there by themselves or that they maintain themselves. Therefore, the difference between us (the believers) and the disbelievers is that we believe in the existence of the Creator of the Universe and they do not.
Please note that you must treat them as a grown up and, as such, use a strong argument that talks to their brain in a compatible way. You must also remember that they are used to be convinced; that is the only way you will be able to get an idea across to them. You must also strive to build a trust between you and your children, such that they will then become more prepared to accept your teaching with confidence.
I have also included some practical steps that you can apply as follows:

  • Establish a halaqa (circle) for Muslims in the same age group as your children. The halaqa’s main purpose is to engage young Muslims in discussing various topics such as angels, prophets, manners in Islam, and so on. This group should have one adult mediator who directs its conduct.
  • Get them actively involved in this group and prepare some material around the topic in discussion; everyone can present their findings and work.
  • Get themm videos on stories from Qur’an and stories of the prophets; encourage them and the whole family to watch them. Make sure that these materials are of a high standard—you do not want to risk boring him. Be prepared, and educate yourself on all the contents of the story beforehand, as they will ask questions (children are very inquisitive). If you can’t answer them on the spot, make it an assignment (little project) for both of you to find the answer from the Qur’an and Hadith with the aid of Islamic books you trust.
  • Bedtime is a good time to tell stories, so you can read to them about the manners of the little Muslims from selected stories. Also, recite the du`aa’ (supplication) to be said before sleep. If they asks you why he should say it, tell him that it will protect them against bad dreams and so on. Always reassure them with kindness and an encouraging smile that what you are saying is the truth and that he is on the right path.
  • Encourage them to memorize parts of the Qur’an, get them to watch videos of the Qur’anic competitions of Saudi Arabia or UAE and they will then see children about his age that memorize the Qur’an and read it in such beautiful voices. It is important to create some peer competition to balance the peer pressure they may be getting from school. You can also get little stickers to stick in his room to encourage them further.
  • Get some posters showing the Pillars of Islam (for children) and, for instance, how to make wudu’ (ablution) and so on.

Finally, I advise you to be patient with them as they may come back from school with lots of myths about Islam and the history of mankind, stories of the prophets and Darwinian theories, the list is endless. You must be very logical with them, but after you have made all this background work it will be easier to convince them, in sha’ Allah, with the right message. You have to listen to what he says, no matter how silly and outrageous. Try to correct misunderstanding with wisdom and logic.