Saint Paul observes how faith is normally passed to children when he says in 2 Timothy 1:5, “I am reminded of your sincere faith, which first dwelt in your grandmother Lois and your mother Eunice, and I am convinced is in you as well.”
It is normal for parents to want their children to be given the best. This motivates parents to teach children proper manners, linguistic skills, social norms, academic subjects and so forth. What greater gift is there than relationship with God (faith)? We were created for that gift and only that gift will fulfill our deepest longings. If parents want their children to be truly happy then they will pass on the gift of faith.
Of course, one cannot give what one does not have. So parents must first be deeply immersed in a relationship with God so they have something to share with their children.