Childishness

Thomas Aquinas, Summa Theologiae 2-2.142.2 co. (my rough translation):

Something is said to be childish (puerile) in two ways. (I) Because it is appropriate to a child. And in this way the Philosopher is not trying to say that the sin of intemperance is childish. (II) According to some sort of likeness. And in this way sins of intemperance are said to be childish. For the sin of intemperance is a sin of excess craving (concupiscentiae), which is likened to a child in three ways.

(1) Inasmuch as it desires something, for, like the child, so also craving desires something ugly (turpe). The reason for this is that beauty is recognized in human things insofar as something is ordered according to reason, wherefore Tully says, in I Offic., "Beauty is what is in accord with human excellence in those things in which his nature differs from other animals." But a child does not pay attention to rational order, and similarly craving does not listen to reason, as is said in VII Ethic.

(2) They are appropriate to each other as to effect. For the child, if left to his own will, grows in self-will; thus it is said in Eccli. XXX, "The untamed horse becomes obdurate, and the lax son becomes headstrong." So also craving, if it is indulged, becomes stronger; thus Augustine says in VIII Confess., "Lust served is made into custom, and custom unresisted is made into necessity."

(3) As to the remedy applied to each. For the child is improved by being limited, wherefore it is said in Prov. XXIII, "Do not withhold discipline from a child; with your rod strike him and free his soul from hell." And likewise when craving is resisted, it is brought back to what worthiness requires (reducitur ad debitum honestatis modum). And thus Augustine says, in VI Musicae, that, the mind being fixed on spiritual things and remaining there, the momentum (impetus) of custom, that is to say of carnal craving, is shattered, and suppressed, it bit by bit is extinguished, for it was greater when we followed it, and though not wholly annihilated, it is surely less when we restrain it. And thus the Philosopher says, in III Ethic, that as a a child ought to live according to the precept of his teacher, so also the desiring part (concupiscibile) ought to harmonize with reason.