Catechism of the Catholic Church §526 — excerpt
To become a child in relation to God is the condition for entering the kingdom. For this, we must humble ourselves and become little. Even more: to become "children of God" we must be "born from above" or "born of God".
This translation is under copyright, so only the cited words are quoted here. Follow the link for the full text. Translation: English translation of the Catechism of the Catholic Church, 2nd ed. (Libreria Editrice Vaticana), as posted at vatican.va.
Whole chapters cited: John 3
Also cites: LH, 1 January, Antiphon I of Evening Prayer