It is true that I was thinking primarily of the writings of Ignatius. The theories about interpolations to his writings are, I think, theoretical, but I am no expert on patristics so as to assess their genuineness. I would like to believe that Ignatius did not write his letters, so that I would not have to believe the church degenerated so quickly into the institutionalism found in them. There is no question that, as the letters stand today, they assume the institution of monarchial bishops.I know of no other writings prior to 200 A.D which "favored infant baptism, monarchial bishops and eucharistic transubstantiation." Or even one of these three.
Ignatius (or Pseudo-Ignatius) wrote: "I desire the bread of GOD, which is the flesh of Jesus Christ" (Epistle to the Romans, 7), and identified as "heretics" those who "confess not the Eucharist to be the flesh of our Savior Jesus Christ, which suffered for our sins" (Epistle to the Smyrnaeans, 7).
Apart from the alleged writings of Ignatius, the idea that the early church held transubstantiation is indeed tenuous, but there are some additional witnesses.
Justin Martyr (c.150) wrote that "we [have] been taught that the food which is blessed by the prayer of His word, and from which our blood and flesh by transmutation are nourished, is the flesh and blood of that Jesus who was made flesh" (First Apology, LXVI). Admittedly, this could be taken non-literally, and, in his Dialogue With Trypho (ch.70), he seems to take the view that it is primarily a memorial of the flesh and blood of Christ—perhaps not literal.
Tertullian (c.200) wrote: "Taking bread and distributing it to his disciples he made it his own body..."(Against Marcion IV. 40). Again, Tertullian's language could be symbolic too.
Roman Catholics appeal to the above for their claims that transubstantiation was the early opinion of the fathers.
The claims that infant baptism was practiced from earliest times is made by Origen (185–254): "The Church had a tradition from the Apostles, to give baptism even to infants" (Commentary on Romans 5.9). He also wrote: "Baptism according to the practice of the Church is given even to infants" (Homilies on Leviticus 8.3.11) and "Infants are baptised for the remission of sins . . . That is the reason why infants too are baptised" (Homily on Luke 14.5).
Irenaeus (130–202) also spoke of infants being "born again to God" (Against Heresies 2:22:4), which, given the connection in the minds of the early believers between rebirth and baptism, probably refers to the latter.
If Ignatius' writings are genuine (about which you have raised legitimate doubts) then all three doctrines—monarchial bishops, transubstantiation and paedobaptism—were taught and practiced in the early church. This does not mean that I believe in any of these doctrines. That was my point to Homer, namely, that we can not always trust that the understanding of the church fathers represents the only, or best, interpretation of New Testament teachings.