It can be either. A baptism may be carried out during a mass or at a ceremony apart from the mass.
In the Catholic church, the priest will ask "what do you ask of God's church for your child?" The response is "Baptism"
The churches that practice infant baptism as a sacrament of initiation into the Christian faith include the Roman Catholic Church, Eastern Orthodox Church, Anglican Church, Lutheran Church, and some Methodist and Presbyterian denominations.
Baptism is still important to us today because it initiates us into the Christian church.
In Christianity, Baptism symbolizes a spiritual "rebirth" into the christian faith, and it is often used as an initiation into a church.
No matter what age, Baptism
A: Either by Infant Baptism and gradual introduction to the Church while growing up or by Adult Baptism after introduction to the Faith.
Some differences here and there -eucharist -sacraments -holidays
The practice of infant baptism began in the early Christian church, around the 2nd century AD.
First off, Catholicism is the first and foremost Christian religion as founded by Christ. As to your question, you can only be baptized once. If done properly, the Catholic Church recognizes the baptism as valid. If the Church is uncertain if a person was validly baptized, that person will receive a conditional baptism. "If you were not baptized before, I baptize you in the name of . . . ."
The practice of sprinkling baptism began to be used in the Christian church around the 3rd century AD as an alternative to full immersion baptism.
Baptism always included in Christian initiation because it is accomplished by means of the sacraments which establish the foundations of Christian life,but Christian initiation not only hold the Baptism but to other sacraments of the church also. The faithful born anew by Baptism are strengthened by Confirmation and are then nourished by the Eucharist.
In this service from a spiritual point of veiw, the baby is accepted into the church community and will show it by receiving all the sacraments following baptism like confession, communion or confirmation. The baptism is just the first step to a Catholic being part of the church.