Let the little children come to Me, and do not forbid them; for of such is the kingdom of God. (Lk. 18:16)

And this age is weak in strength, feeble in intelligence, and immature in counsel. Thus, age is not preferred to age; moreover, it would be hurtful to grow up. What need is there for prayers that maturity of age ensue, if it is to take from me the merit of the Heavenly Kingdom? So did God give the course of life for vices and not for the increase of virtue? And why did He choose Apostles who were not youthful, but of mature years? But why does He say that children are fit for the Kingdom of Heaven? Perhaps, because they do not know malice, they have not learned to deceive, they dare not strike back, they neglect to search for wealth, they do not strive after honor and ambition.

But virtue is not to be ignorant of those things, but to despise them, nor is there praise of abstinence where there is integrity through weakness. For not childhood, but goodness rivaling childlike simplicity is meant. For it is not a virtue to be unable to sin, but to be unwilling so to do and to retain perseverance of will, so that the will imitates childhood and one man imitates nature. Finally, our Saviour Himself expressed this saying: Unless ye be converted, and become as this boy, ye shall not enter into the Kingdom of the Heavens. (Mt. 18:3)

St. Ambrose of Milan