Since I was already researching the history behind the christening gown, I thought it might be interesting to research the christening ceremony. I was not familiar with the background, since I'm a Baptist - cough.
The christening/baptism ceremony was mandated by the Catholic church in 416, and the edict was written that all babies that died before being baptised would enter limbo. (This was later lifted in 2007 when the Pope proclaimed that all babies and children went to heaven, baptized or not.)
The baptism ceremony removes sins and unites the child as a child of God and a member of the Catholic church. The parents and godparents take a part in the ritual - the godparents promise to see after the child's religous training, and his/her progress through life.
The white christening gown is a sign of Christian dignity and purity, the oil placed on the head and chest in the sign of the cross is the Holy Spirit, and the lit candle is symbolic of the light of Christ, which we are all asked to keep lit.