Remember, the first Bodhisattva Vow is to deliver innumerable sentient beings. Your children are sentient beings. How can you best do this? In addition to providing the basic care for children ─ providing a good education, helping them become useful members of society ─ you should also be concerned with the psychological states of mind of your children. Can you show them how to have peace of mind? Can you help them understand and accept the Three Jewels? Can you introduce them to and help them with methods of practice? If you can do these things, then you have done all you possibly can do.
We live in a hectic society. It is heterogeneous, not homogenous. It is constantly changing. It's confusing enough for the parents. Instead of telling children what they should or shouldn't do, you should explain what you are doing in a given situation, and why you are doing it You should try to explain why others do what they do. Don't make judgments for children, just try to help them understand. If you can do this, then probably, your children will, of their own accord, turn to Buddhadharma.
It's good to do these things before children reach fourteen or fifteen years of age. If you start early, then it will be easy for your children to develop faith in Buddhism. But if you wait beyond this age, it will be difficult for children to develop the same kind of faith. Besides, around this time, children will begin to rebel against you, so it's better to get most of your teaching out of the way before that happens.
Adults who turn to Buddhadharma are rare. Why they turn to Buddhism varies, but usually, it's because they find something lacking in their previous faiths, and in coming in contact with the Dharma, they feel an attraction toward it. It is the result of previous good karma. It's also a rational, conscious decision by the person. Most people, however, do not change.
If you haven't succeeded in interesting your children in the Dharma by the time they reach adulthood, chances are you're never going to succeed. At that point, they are on their own. Emphasis on teaching the Dharma to your children should begin well before they reach fourteen.