I have given much thought in the past few years as to my spiritual formation as a child. My mother and the nuns taught me my prayers and a great love for Our Lady and her holy rosary and Jesus Our Eucharistic Saviour. However, it was three little Catholic books which I would say have formed my Marian and Eucharistic devotion and piety. St John Bosco says, "only God knows the good that can come about by reading one good Catholic book." St Alphonsus Liguori says, "Without good books and spiritual reading, it would be morally impossible to save our souls."
All three of these spiritual treasures are available online for the edification of everyone:
JESUS OUR EUCHARISTIC LOVE by Father Stefano Manelli, O.F.M. Conv., S.T.D.
THE SECRET OF THE ROSARY by St Louis Grignion de Montfort
THE WHOLE TRUTH ABOUT FATIMA (MOTHER OF CHRIST CRUSADE)