Thousands of children write letters to Santa Claus, telling him all the toys and goodies that they want for Christmas every year. It started during the mid-20th century.
The modern tradition of Christmas letters is focused solely on St. Nick. But in the pioneer times, these letters were addressed to the Christ Child.
Francis Xaver Weiser explains the Christmas custom in his book Handbook of Christian Feasts and Customs.
When the children go to bed on the eve of St. Nicholas’s Day (December 5), they put upon the window sills little notes that they have written or dictated, addressed to the Child Jesus. These letters, containing lists of desired Christmas presents, are supposed to be taken to heaven by Saint Nicholas or by angels.
According to Weiser, there is also a tradition in South America where “the children write their notes to the ‘little Jesus’ during the days from December 16 to 24 and put them in front of the crib, whence, they believe, angels take them to Heaven during the night.”
This custom is a perfect way to “Christianize” the children’s desire to write letters to Santa Claus. It helps direct children to the Christ Child, while also honoring the existence of St. Nicholas, who, being in Heaven, would be perfectly suited as an intercessor.