This is incorrect. The definition of Baptism of Desire presupposes a human act (that is, an act involving reason) on the part of the person to be baptized. This is the only possible interpretation of the teachings of the Church and her Doctors and theologians. Baptism of Desire is de fide doctrine, and this de fide doctrine is described by St. Alphonsus Liguori:
“Perfect conversion to God through contrition or love of God above all things, with the explicit or implicit desire [voto] for true Baptism of water, in whose place it may supply, according to the Council of Trent.”
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"It is de fide that men may be also be saved through baptism of desire — from the chapter Apostolicam, de presb. non bapt. and from the Council of Trent, where it is said that no one can be saved ‘without the washing of regeneration or the desire for it’.” (Theologia Moralis, ed. nova. [Rome: Vatican 1909] 3:96-7)
The 2nd and 3rd methods you mentioned are contrary to de fide doctrine; they are heretical.
The logical conclusion from this is that these infants have the built-in capacity to commit mortal sin. If they have the ability to love God and to will to receive Baptism, then they also have the ability to reject Him by committing mortal sin.
God doesn’t usually work outside the natural order He establishes, whether it’s in regard to the natural life (as in the use of reason) or to the supernatural life (as in the means of salvation). To say otherwise is basically to say He changes His mind or made a mistake He needs to undo; I mean, why didn’t He establish a different order in the first place so He doesn’t have to make all those exceptions?
Saying that He infuses reason into these infants is saying that exceptions are the norm. Why did He even establish the necessity for human acts in Baptism of Desire if so many millions and millions of times He has to intervene in the natural order to make this possible for those who would not be able to make those human acts? Why didn’t He just do away with that necessity altogether or at least make it conditional on whether the individual in question actually has the use of reason?
Maria