A will ensures that your valuable earthly possessions will go to your children. But what about heavenly possessions? Begin preparing these gifts before your children consciously understand - pass on your faith through prayer, Bible reading and meditation, and otherwise bringing up your offspring in the fear and nurture of the Lord. Otherwise, you may pass on your wealth but not your Treasure.
Do you blame others for your children's loss of faith, should that ever occur? Or do you rightly blame yourself? With all our idols, the failure is our own. But the forgiveness is God's! He intervenes, breathing new life into us in our death, reaching around us in our rejection of Him. Receive Him therefore, passing your faith down to the next generation.
Let His commandments first be upon your heart. Then constantly and consistently impress them on your children's hearts. Just as immersion leads to fluency because you leave your native language behind, so also it works with the Word. Even before your children understand, talk - not *to* your kids but just *about* the Word. Immerse yourself and your spouse in this Word. The children's immersion will follow.
Pray with and for your children. This is the Holy Spirit's work - creating faith and interceding for us. The entire home environment is important as well. Also, show your children how and why to share your faith. Show by your words and deeds the totality of God's love. God uses people as His hands. What are we, save vessels to be filled with and to share God's love?
Finally, remember that our best-laid plans will fail. But God still works.
Soli Deo gloria.