The home is the natural environment for initiating a human being into solidarity and communal responsibilities. Parents should teach children to avoid the compromising and degrading influences which threaten human societies. (Catechism of the Catholic Church #2224)
Since parents have given children their life, they are bound by the most serious obligation to educate their offspring and therefore must be recognized as the primary and principal educators. This role in education is so important that only with difficulty can it be supplied where it is lacking. Parents are the ones who must create a family atmosphere animated by love and respect for God and man, in which the well-rounded personal and social education of children is fostered. Hence the family is the first school of the social virtues that every society needs. (Declaration on Christian Education Gravissimum Educationis by Pope Paul VI.)
Train a child in the way he should go; even when he is old, he will not swerve from it. (Proverbs 22:6)
"If I had to advise parents, I should tell them to take great care about the people with whom their children associate...Much harm may result from bad company, and we are inclined by nature to follow what is worse than what is better." (St. Elizabeth Ann Seton)