Sources for baptismal exorcism of infants?

As I said in my comment this is tough to answer. Early Christians like emperor Constantine often put off their baptism: because, the issue of how sin was dealt with after baptism was not clearly dogmatically defined in the early Nicene era.

9. Let thy feet hasten to the catechisings; receive with earnestness the exorcisms: whether thou be breathed upon or exorcised, the act is to thee salvation. Suppose thou hast gold unwrought and alloyed, mixed with various substances, copper, and tin, and iron, and lead: we seek to have the gold alone; can gold be purified from the foreign substances without fire? Even so without exorcisms the soul cannot be purified; and these exorcisms are divine, having been collected out of the divine Scriptures. Thy face has been veiled, that thy mind may henceforward be free, lest the eye by roving make the heart rove also. But when thine eyes are veiled, thine ears are not hindered from receiving the means of salvation. For in like manner as those who are skilled in the goldsmith’s craft throw in their breath upon the fire through certain delicate instruments, and blowing up the gold which is hidden in the crucible stir the flame which surrounds it, and so find what they are seeking; even so when the exorcists inspire terror by the Spirit of God, and set the soul, as it were, on fire in the crucible of the body, the hostile demon tees away, and there abide salvation and the hope of eternal life, and the soul henceforth is cleansed from its sins and hath salvation. Let us then, brethren, abide in hope, and surrender ourselves, and hope, in order that the God of all may see our purpose, and cleanse us from our sins, and impart to us good hopes of our estate, and grant us repentance that bringeth salvation. God hath called, and His call is to thee.

Catechism lecture Prologue, Cyril of Jerusalem

Cyprian: "The obstinate wickedness of the devil prevails even up to the saving water, but that in baptism it loses all the poison of his wickedness...when, however, they come to the water of salvation and to the sanctification of baptism, we ought to know and to trust that there the devil is beaten down, and the man, dedicated to God, is set free by the divine mercy. For as scorpions and serpents, which prevail on the dry ground, when cast into water, cannot prevail nor retain their venom; so also the wicked spirits, which are called scorpions and serpents, and yet are trodden under foot by us, by the power given by the Lord, cannot remain any longer in the body of a man in whom, baptized and sanctified, the Holy Spirit is beginning to dwell" (Epistle 75:15).

Sadly, I don't think any lengthy treatises were written on what your asking for. The quotes I've run across with multiple searches simply reveal statements of a paragraph or two that you probably already have read. But this should not be surprising ;because, the Church had bigger fish try as far with various dogmatic battles with heretics, defining Christology and so on. Besides this there is a reason that comes to mind from discussions and essays of iconography. Satan and the demons are generally only depicted in profile because while the iconographer wants to acknowledge their presence, it is best to contemplate the things that edify us (Philippians 4:8)

Post from Aquinas' Summa Theologica, where he quotes Pope Celestine circa 422 AD:

Article 2. Whether exorcism should precede Baptism? Objection 1. It seems that exorcism should not precede Baptism. For exorcism is ordained against energumens or those who are possessed. But not all are such like. Therefore exorcism should not precede Baptism.

Objection 2. Further, so long as man is a subject of sin, the devil has power over him, according to John 8:34: "Whosoever committeth sin is the servant of sin." But sin is taken away by Baptism. Therefore men should not be exorcized before Baptism.

Objection 3. Further, Holy water was introduced in order to ward off the power of the demons. Therefore exorcism was not needed as a further remedy.

On the contrary, Pope Celestine says (Epist. ad Episcop. Galliae): "Whether children or young people approach the sacrament of regeneration, they should not come to the fount of life before the unclean spirit has been expelled from them by the exorcisms and breathings of the clerics."

I answer that, Whoever purposes to do a work wisely, first removes the obstacles to his work; hence it is written (Jeremiah 4:3): "Break up anew your fallow ground and sow not upon thorns." Now the devil is the enemy of man's salvation, which man acquires by Baptism; and he has a certain power over man from the very fact that the latter is subject to original, or even actual, sin. Consequently it is fitting that before Baptism the demons should be cast out by exorcisms, lest they impede man's salvation. Which expulsion is signified by the (priest) breathing (upon the person to be baptized); while the blessing, with the imposition of hands, bars the way against the return of him who was cast out. Then the salt which is put in the mouth, and the anointing of the nose and ears with spittle, signify the receiving of doctrine, as to the ears; consent thereto as to the nose; and confession thereof, as to the mouth. And the anointing with oil signifies man's ability to fight against the demons.

Reply to Objection 1. The energumens are so-called from "laboring inwardly" under the outward operation of the devil. And though not all that approach Baptism are troubled by him in their bodies, yet all who are not baptized are subject to the power of the demons, at least on account of the guilt of original sin.

Reply to Objection 2. The power of the devil in so far as he hinders man from obtaining glory, is expelled from man by the baptismal ablution; but in so far as he hinders man from receiving the sacrament, his power is cast out by the exorcisms.

Reply to Objection 3. Holy water is used against the assaults of demons from without. But exorcisms are directed against those assaults of the demons which are from within. hence those who are exorcized are called energumens, as it were "laboring inwardly."

Or we may say that just as Penance is given as a further remedy against sin, because Baptism is not repeated; so Holy Water is given as a further remedy against the assaults of demons, because the baptismal exorcisms are not given a second time.