Thank you. That one sentence led me to a google search and I found this:
Polycarp (69-155), a disciple of the Apostle John, was baptized as an infant. This enabled him to say at his martyrdom. “Eighty and six years have I served the Lord Christ” (Martyrdom of Polycarp 9: 3). Justin Martyr (100 - 166) of the next generation states about the year 150, “Many, both men and women, who have been Christ’s disciples since childhood, remain pure at the age of sixty or seventy years” (Apology 1: 15). Further, in his Dialog with Trypho the Jew, Justin Martyr states that Baptism is the circumcision of the New Testament.
Irenaeus (130 - 200), some 35 years later in 185, writes in Against Heresies II 22: 4 that Jesus “came to save all through means of Himself - all. I say, who through him are born again to God - infants and children, boys and youth, and old men.”
mtio.com/articles/aissar40.htm
There is early writings by our apostles successors, the early Church fathers, who show infant baptism was practiced in the early Church.
“For He came to save all through means of Himself – all, I say, who through Him are born again to God – infants, and children, and boys, and youths, and old men.”
(IRENAEUS, Adversus haereses, Book 2, Chapter 2:4 [A.D. 178])
“Baptize first the children; and if they can speak for themselves, let them do so. Otherwise, let their parents or other relatives speak for them.”
(HIPPOLYTUS, The Apostolic Tradition [A.D. 215])
"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, Homilies on Leviticus, Homily 8, 3 [A.D. 185-253])
The Church received from the Apostles the tradition of giving Baptism even to infants. For the Apostles, to whom were committed the secrets of divine mysteries, knew that there is in everyone the innate stains of sin, which must be washed away through water and the Spirit.
(ORIGEN, Commentaries on Romans 5:9 [A.D. 185-253])
(NOTE: At the end of this article is a photo of the carving of a child being baptised which is on the wall of a catacomb, as was reported in the post to which I have responded here (although it was reported to be an infant and the engraving is obviously not of an infant but a child; there may be more carvings.))
kathyschley.com/Catholic_Churc/infantbaptism.html