Why do Catholics believe babies need to be baptized?
Because babies are born with original sin, they need baptism to cleanse them, so that they may become adopted sons and daughters of God and receive the grace of the Holy Spirit. Jesus said that the kingdom of God also belongs to children (see Mt 18:4; Mk 10:14).
Infant Baptism has been practiced since apostolic times. Infants need to be baptized because through this Sacrament, they are freed from Original Sin and are welcomed into the community of the Church, where they have access to the fullness of the means of salvation.
Some supporters of infant baptism believe that baptism has almost magical power to save and that a baby who dies unbaptized cannot go to heaven. They think the water itself washes away the original sin a baby is born with and causes a baby to be born again into new life.
It does not in any way convey the grace it symbolizes; rather, it is merely a public manifestation of the person's conversion. Since only an adult or older child can be converted, baptism is inappropriate for infants or for children who have not yet reached the age of reason (generally considered to be age seven).
Short answer: yes!
Why does the Catholic Church baptize infants? So they can be united into the community of faith. The gift of baptism doesn't have any requirements so it is open to anyone, it's their entry to Christian life.
There is no certain evidence of this practice earlier than the 2nd century, and the ancient baptismal liturgies are all intended for adults. There is, however, extensive testimony suggesting the introduction of infant baptism as early as the 1st century.
Acts 2:38 says, “Repent and be baptized every one of you in the name of Jesus Christ for the remission of sins, and you shall receive the gift of the Holy Spirit.” Baptists say repentance is a clear prerequisite to baptism here. An infant cannot repent, therefore an infant cannot be baptized.
The fate of unbaptized babies has confounded Catholic scholars for centuries. According to church catechisms, or teachings, babies that haven't been splashed with holy water bear the original sin, which makes them ineligible for joining God in heaven.
Limbo is the nether region where, according to Roman Catholic tradition, unbaptized babies go after death. It's a pleasant enough place, though devoid of the bliss of God's presence.
How do you explain that Catholic baptism is not only for babies?
Because baptism is the Sacrament in which God forgives original sin (Baptism forgives ALL sins, but as an infant, they only have original sin 5). Original sin is passed down from generation to generation by birth.
Some people would agree that infant baptism is not as important as believers baptism. This is because when you are an adult you can make your own choice whether you want to enter a religion or not as you have more of an understanding of what you are signing up for than when you are a baby.

She wrote, accurately, that Protestants who don't baptize infants consider this an “ordinance” and not a “sacrament,” so that the ceremony symbolizes the individual's new life in Christ with personal profession of faith.
Since a person is saved by the gospel (Ro- mans 1:16), which does not include baptism (1 Corinthians 1:17; 15:3– 4), then a person can be saved without being baptized. All that is nec- essary is for a person to hear the gospel and trust Jesus Christ for eter- nal life.
The nature of baptism is that of a public act. When a new believer is baptized, he or she is giving a public testimony of his or her faith in Jesus as others are witnessing this public identification with Christ and the Christian church.
Baptists conduct “believer's baptism,” as opposed “infant baptism,” because they believe that only people who confess their sins and profess faith in Christ should be baptized. This rules out baptizing infants because of their inability to hold and express these convictions.
There is no age limit, but infants are generally baptized between three and six months old. Children who are 7 years old or older must participte in the RCIC classes to prepare them for baptism.
Conversely, for those who support infant baptism, they say baptism is God's way of saying "you are mine." In other words, baptism is a sign of God's covenant with us. And all throughout the Bible, when God makes a covenant with an parent, he is making that covenant with the children.
Baptism seals the Christian with the indelible spiritual mark (character) of his belonging to Christ. No sin can erase this mark, even if sin prevents Baptism from bearing the fruits of salvation. Given once for all, Baptism cannot be repeated.
Go therefore and make disciples of all nations, baptizing them in the name of the Father and of the Son and of the Holy Spirit, teaching them to observe all that I have commanded you. And behold, I am with you always, to the end of the age (Matthew 28:18-20).
Is it right to baptise babies?
The scriptures teach that “little children are alive in Christ, even from the foundation of the world” (Moroni 8:12). God is merciful, loving, and kind. He wants all of His children to return to live with Him. He would not be the loving and just God that He is if He denied children salvation for not being baptized.
I believe that God is clear in Scripture that He welcomes into heaven each baby who dies, born or unborn (Ps 139). And this extends to young children and the mentally disabled who die before they are able to understand salvation. God is not silent on this question.
The answer finally came when the Lord described how parents should teach their children about the gospel. He said, “And their children shall be baptized for the remission of their sins when eight years old, and receive the laying on of the hands” (Doctrine and Covenants 68:27).
It was known variously as the "ground of the holy innocents" or as the children's section. Only baptized Catholics could be buried in consecrated ground. Even if a family had a plot in a Catholic cemetery, a baby who died without having been baptized had to be buried in the special section.
The Catholic Church holds that "all who die in God's grace and friendship but still imperfectly purified" undergo a process of purification, which the Church calls purgatory, "so as to achieve the holiness necessary to enter the joy of heaven".