11 For this reason the Council of Trent, treating of the duties of pastors of souls, decreed that their first and most important work is the instruction of the faithful. It therefore prescribes that they shall teach the truths of religion on Sundays and on the more solemn feast days; moreover during the holy seasons of Advent and Lent they are to give such instruction every day or at least three times a week. This, however, was not considered enough. The Council provided for the instruction of youth by adding that the pastors, either personally or through others, must explain the truths of religion at least on Sundays and feast days to the children of the parish, and inculcate obedience to God and to their parents. When the Sacraments are to be administered, it enjoins upon pastors the duty to explain their efficacy in plain and simple language.
Source: Acerbo Nimis (Vatican.va)