Infant baptism was never a first century Christian practice.
Where does it say that in Scripture? It’s not even implied that infants were excluded from baptism, let alone stated explicitly that they were excluded from baptism.
What is implied in scripture is that whole households and families were baptised, this would include infants.
Middle eastern households even today aren’t nuclear, and are loaded with infants, this was doublely so in Apostolic times.
Next we have the testimony of all the Early Christians themselves saying that it was universally a Christian Church practice continually done from the Apostles.
“[T]herefore children are also baptized.” Origen, Homily on Luke, XIV (A.D. 233).
“For this reason, moreover, the Church received from the apostles the tradition of baptizing infants too.” Origen, Homily on Romans, V:9 (A.D. 244).
“Baptism is given for the remission of sins; and according to the usage of the Church, Baptism is given even to infants. And indeed if there were nothing in infants which required a remission of sins and nothing in them pertinent to forgiveness, the grace of baptism would seem superfluous.” Origen, Homily on Leviticus, 8:3 (post A.D. 244).
“And if any one seek for divine authority in this matter, though what is held by the whole Church, and that not as instituted by Councils, but as a matter of invariable custom, is rightly held to have been handed down by apostolical authority, still we can form a true conjecture of the value of the sacrament of baptism in the case of infants, from the parallel of circumcision, which was received by God’s earlier people, and before receiving which Abraham was justified, as Cornelius also was enriched with the gift of the Holy Spirit before he was baptized.” Augustine, On Baptism against the Donatist, 4:24:31 (A.D. 400).
The only controversy in Early Christianity regarding infant Baptism was when the child was to be baptised.
It was suggested by some that infants should be baptised on the eighth day as was customary with the Jewish practice of circumcision.
But the heads of the churches decided that it should be done immediately without delay in case of death, because Baptism was always seen as regenerational.
“The blessed Cyprian, indeed, said, in order to correct those who thought that an infant should not be baptized before the eighth day, that it was not the body but the soul which behoved to be saved from perdition — in which statement he was not inventing any new doctrine, but preserving the firmly established faith of the Church; and he, along with some of his colleagues in the episcopal office, held that a child may be properly baptized immediately after its birth.” Augustine, Epistle 166:8:23 (A.D. 412).