It is in the home that children ordinarily first receive the faith
One of the documents of the Second Vatican Council, Lumen Gentium (“Light of the Nations”), describes the family as the ‘domestic Church’ because it is the first place where young, baptized Christians learn about their faith. It states, “From the wedlock of Christians there comes the family, in which new citizens of human society are born, who by the grace of the Holy Spirit received in baptism are made children of God, thus perpetuating the people of God through the centuries” (Lumen Gentium, 11). You may have heard it said that families are the fundamental ‘building block’ of society; similarly, families provide a foundation for the continuation and strength of the Church among the lay faithful.
Lumen Gentium goes on to explain that this domestic Church has a particular role and responsibility in leading souls to heaven: “In it parents should, by their word and example, be the first preachers of the faith to their children; they should encourage them in the vocation which is proper to each of them, fostering with special care vocation to a sacred state” (Ibid). Through this letter, the Council Fathers intended to emphasize that Christ is the Light of the Nations, and that, as the Church, we each have a responsibility to bring the Light of Christ to others. Within the domestic Church, this means that parents are to cultivate a family life that is centered on Christ.
The United States Council of Catholic Bishops (USCCB) provides some helpful ways that families can live out their vocation as the domestic Church. Suggestions include praying as a family daily, keeping physical reminders of faith (such as a crucifix) in the house, and celebrating the liturgical feasts of the Church. You may find more recommendations here.
The Catholic Church recognizes that grace builds upon nature. Family is one of the most basic, yet important gifts that God has given us. Through a firm marital commitment between men and women, and through their own active participation in the faith and their pledge to raise their children with a love for Christ and his Church, the domestic Church is one of first places that young Catholics experience the light of the faith in their own lives.