Cap. IX Arg. 11 Sol: Augustine on sacrament preceding heart-conversion; Fulgentius — baptism suffices for infants while reason is incapable; Aquinas — Christ's passion applied by the sacrament
Finally, on adults' actual renewal or regeneration — when by the power of divine word and Spirit one is converted and by believing justified — Augustine writes: In baptized infants the sacrament of regeneration precedes, and if they hold Christian piety, conversion of heart also follows, whose mystery preceded in the body (lib. 4 Contra Donatist. Cap. 24). So of all baptized infants we assert with Fulgentius: The sacrament of faith, which is holy baptism, while infants' age cannot be capable of reason, suffices them for salvation (De fid. ad Petrum Diac. Cap. 30). Nor do we scorn Aquinas on this: Infants who have nothing reby they can turn themselves to the justifying cause have that cause itself — Christ's passion — applied to them through the sacrament of baptism (Quaest. disp. de Justific. Art. 3).
Latin
Denique, de renovatione sive regeneratione actuali adultorum, quae fit cum quis virtute verbi Divini Spiritusque convertitur, et credendo justificatur, sic scribit Augustinus, In baptizatis infantibus praecedit regenerationis sacramentum, et si Christianam pietatem tenuerint, sequitur etiam in corde conversio, cujus mysterium praecessit in corpore, lib. 4. Contra Donatist. cap. 24. Nos itaque de omnibus infantibus baptizatis cum Fulgentio asserimus, Sacramentum fidei, quod est sanctum baptisma, quamdiu rationis aetas infantium capax esse non potest, sufficit eis ad salutem, De fid. ad Petrum Diac. cap. 30. Neque Aquinatis hac de re dictum adspernamur; Qui, inquit, non habent infantes unde possint se convertere ad causam justificantem, ipse causa justificans, scilicet passio Christi, applicatur eis per sacramentum baptismi, Quaest. disp. de Justific. art. 3.