In the Catholic Church, First Holy Communion is held in high regard because of the Eucharist as the source and summit of our faith. On this day, your child will be meeting the Lord in this Sacrament. Therefore, your son or daughter should be dressed to the best of their ability to greet the Lord in reverence.
White is the symbol for purity in the Church. Wearing white on First Communion Day is reminiscent of the white gowns worn at the Sacrament of Baptism, when your child first entered the Catholic faith.
Traditional attire for boys is either a dark suit with a white shirt, or a white suit.
Traditional attire for girls is a white dress and veil. The veil hearkens back to the days when women always covered their heads at Mass, which was a standard until a few decades ago. Some traditions hold that the veil represents the tablecloth at the Last Supper, while the white dress represents the clothing that Jesus wore that evening. White shoes and tights are common, and sometime young ladies like to wear white gloves.
When dressing for First Communion Day, modest and chastity should always be kept in mind. Reverence for this gift of Jesus — the gift of Himself — is a joyous occasion in the life of every young Catholic. You can find great Catholic apparel here.