To clothe oneself in Christ is what the handing over of a garment to the newly baptized signifies. In the Bible, white is the color of God.
In practice, it is very complicated to put a christening gown on a baby who is crying because water has just been poured on their head and who is wriggling because the ceremony is long for them, not to mention that there is no changing table and it can be cold!
Parents often choose to dress their child in the christening garment before the ceremony begins. However, in this case, it is important to remember to provide an additional white garment, such as a bonnet or a stole, which will be given to the godparents so that it can be placed on the baby once the priest has baptized them.
For purists, eager to follow tradition, you can request a christening gown that is completely open at the back, just buttoned at the back of the bodice, so that it can be put on somewhat like a coat over the baby's clothes.