Baptism is one of the sacraments of the Church and is often viewed as a welcoming ordinance into a Christian community. When a baptism takes place there are a number of symbols that are associated with the ordinance. They are white clothing, the cross, oil, light, water, and the dove.
The color white is symbolic of cleanliness, purity, virtue, and holiness. This is why christening gowns are almost always white. The wearing of a white christening gown symbolizes that the person being baptized is clean before God. Christians believe, with a few exceptions (The Church of Jesus Christ of Latter-Day Saints) that everyone is born with "original sin" which can only be washed away by being baptized. Once baptized the person is now clean from sin and ready to start a new life.
Most Christians view the cross as a symbol of christianity. When the sign of the cross is made over a child during baptism it invokes protection from God.
During a baptism, oil is symbolic of bringing a person and the Holy Spirit together.
Light is represented in the form of a candle during a baptism. This candle is symbolic of moving from death to life in Christ. It is also symbolic of Christ being "the light of the world."
"...Unless a man is born of water and of the Spirit, he cannot enter the kingdom of God..." Water is an important symbol in baptism that represents sin being washed away and the person being baptized becoming pure and clean.
Like oil, the dove is a symbol of the Holy Spirit. When Jesus was baptized by John the Baptist the heavens were opened and God spoke saying "Thou are my beloved Son, in whom I am well pleased." After God spoke the Holy Spirit descended in the form of a dove.