What traditions are those, specifically, and how do you know? How is the source verified and how do we know that it was passed down accurately?
Catholics can't point to any Scripture that commands us to baptize infants.
Catholics can't point to any Scripture that says that being baptized puts us into the church.
“What traditions are those, specifically, and how do you know? How is the source verified and how do we know that it was passed down accurately”
well, since the Church received the teachings, you must be taught by the Church to know them.
how do we know they were passed down accurately? The Holy Spirit guides and leads the Church into all truth, as Jesus promised He would.