Family ties are important but not absolute. Just as the child grows to maturity and human and spiritual autonomy, so his unique vocation which comes from God asserts itself more clearly and forcefully. Parents should respect this call and encourage their children to follow it. They must be convinced that the first vocation of the Christian is to follow Jesus: "He who loves father or mother more than me is not worthy of me; and he who loves son or daughter more than me is not worthy of me."
Source: Catechism of the Catholic Church (Vatican.va)