In Acts, it cites an entire family that was baptized together, although we don't know what their ages were. However, we do know that there was some infant baptism that was done during the 2nd century but it wasn't the norm. It did become more common later, especially when one of the plagues hit, thus an estimated 1/3 of Europe's children died.
What the Church did was to recognize the family as a child's source of morality when young, so whereas the father was baptized Christian, the rest of the family followed suit. However, because of the profession of faith that's needed, that was created by splitting baptism into two ceremonies: baptism and confirmation, whereas the latter repeats the baptismal vows.
The Church is and was "apostolic", thus following the lineage of what we call "apostolic succession", and that is rather easily verified by doing some homework. Here, I'll help:
Apostolic succession - Wikipedia
That process one can see rather clearly in Acts and some of Paul's letters whereas the Twelve begin to appoint leaders and, later, successors. That process continued on through the ages even though there were political splits that took place, with the big one taking place in 1054 c.e.-- the Great Schism.
Finally, if one truly regards themselves as being "Christian", then I would assume they would at least try and follow Jesus' teachings, but unfortunately all too many ignore those, such as those who ignore his teaching of "judge ye not...".
Therefore, the idea that those whom are Catholic and whom acknowledge the Pope as their earthly leader are somehow "lost adults" is to stick one's thumb in Jesus' eye. It was that kind of church that taught such bigoted judgmentalism that I left almost 50 years ago because of this and also its anti-science and its racist agendas.
Meanwhile, as we've seen all too often, many self-professed "Christians" do what Paul and Jesus said not to do, namely to attack other Christians, thus causing divisions while strutting around as if they've got all "the answers".