If a father is a model of prayer to his son

 Pope Saint John Paul II's parents, Emilia and Karol Wojtyła

Emilia died when JP II was just 8 years old

The son might become a priest, pope and saint, which is what happened with John Paul II, as Francis Phillips relates here.   John Paul II's dad, Karol, taught by his example of "deep yet unselfconscious piety," praying the rosary with his family, and praying often at other times throughout the day.  And not only during the day; John Paul II would sometimes awaken in the night to find his father praying silently on his knees.

A lesson from a good father can sometimes become unexpectedly deep rooted.  Once, when the young John Paul II was worried about an upcoming exam, Karol taught his son a prayer to the Holy Spirit, instructing him to say it every day.   John Paul II did so, every day, for the rest of his life.

Of course, not every son is meant to become a priest or a pope like John Paul II.  But all children are meant to be saints, and by teaching the habit of prayer every father guides his children along the road to sanctity.