Catechism of the Catholic Church §2225 — excerpt
Through the grace of the sacrament of marriage, parents receive the responsibility and privilege of evangelizing their children. Parents should initiate their children at an early age into the mysteries of the faith of which they are the "first heralds" for their children.
This translation is under copyright, so only the cited words are quoted here. Follow the link for the full text. Translation: English translation of the Catechism of the Catholic Church, 2nd ed. (Libreria Editrice Vaticana), as posted at vatican.va.
Also cites: LG 11 # 2