All of us try to make our children "Good Muslims". Similarly a Christian tries to make his children "Good Christians", an Atheist tries to make his children "Good Athiests". These efforts make a child biased or at least strongly inclined towards a particular religion. When he grows up, he has a strong set of beliefs and practices and he considers all other religions "wrong". He also has strong relations within his family and friends. All these factors make the religious conversion almost impossible. Only those people convert who revolt from their beliefs and society. That is the reason that entire Da'wah activity of any religion faces a lot of problems.
Can we say that this effort is a good ethical practice? If it is a good practice, it means that it is good for Muslims and Non-Muslims and Allah will not punish Non-Muslims for it because they were made biased by their parents and society. If it is a bad practice, it will be bad for both Muslims and Non-Muslims. In this case, as ethical human beings, we should stop this practice. We should teach our children only the agreed-upon ethics to make them good human beings. At their age of maturity, they should be allowed to evaluate different religions in an unbiased manner and adopt whatever they find the best.
Another aspect of this issue is that according to Quran "there is no compulsion in religion". Is this activity of making our children "Good Muslims" a type of compulsion because it creates a bias in their mind. What are teachings of Quran and Sunnah about this practice?
We believe that it is incumbent upon a Muslim to spread the word of God to others and to share the guidance bestowed upon him by the Almighty with other human beings. One's family and near relations do have their right upon us to share whatever light we have been blessed with. This is only natural that the parents impart whatever knowledge they have to their children. This includes their religious affiliation. In fact the religious truth one believes in is the most important knowledge one would be transferring to one's offspring. Abandoning religious education would mean destroying the most important vehicle of the life and continuity of the religion one believes in. The Holy Qur'an frequently refers to this duty. It says:
The age (of Messengers) bears witness that men are in loss. Except for those who believe and do righteous deeds and teach each other the truth and teach each other to remain steadfast (on it). Al-Qur'an 103:1-3
As regards the verse: there is no compulsion in religion, it is not relevant here. The verse says that we cannot compel others to accept faith. It does not say that we cannot teach others what faith is. You are right in saying that it is very difficult for a Christian for example to consider the call of Islam and consider its arguments and check their veracity and then decide to adopt it. The more the difficulty in this way the lesser the duty incumbent upon the people regarding search of truth. Of course such difficulties will be accounted for. That is why we say that the only truth is Islam which one has to follow in order to merit everlasting bliss in the afterlife. But we do not say that the door to the heaven is closed for others. They can enter heaven by following what they know to be the truth and adopting piety and virtue enter the mercy of God. It is however their duty to respond to the call of Islam if they have been approached through any means.
I believe that the practice of teaching the children what one believes in our duty, their right and the only natural practice. Having grown up they can decide to convert to any religion.