Typically, the types of Christian beliefs labeled “once saved, always saved” are associated with Baptist-type churches. Baptists believe that baptism is an ordinance that signifies dying to sin and rising to life in Christ. It is believed to be symbolic as Baptists don’'t believe in baptismal regeneration.
What regenerates, from the Baptist point of view, would be faith in Christ and repentance from sin. Often, churches might encourage new converts to pray a “sinner’s prayer” which is a prayer expressing one’s faith in Christ and repentance. Baptists may consider this moment the time when they were born again or in common speech “saved.”
Now, another type of church group that might be included within the “once saved, always saved” teachings are certain Presbyterian/Reformed churches. These do practice infant baptism, but they believe in the doctrine of unconditional election. The baptism is a “sign and seal” of the covenant, but that person would still need to come to faith in Christ later in life. If someone is not one of the elect and was baptized, then they would still remain one of the non-elect. In the Reformed view, baptism is only beneficial for the elect.