The tradition of the giving St. Nick comes from a story of a poor man who had three daughters for whom he did not have money for a dowry... well here, let me quote from another site:
The most famous story about St. Nicholas tells how the custom of hanging up stockings to get presents in first started! It goes like this:
There was a poor man who had three daughters. He was so poor, he did not have enough money for a dowry, so his daughters couldn't get married. (A dowry is a sum of money paid to the bridegroom by the brides parents on the wedding day. This still happens in some countries, even today.) One night, Nicholas secretly dropped a bag of gold down the chimney and into the house (This meant that the oldest daughter was then able to be married.). The bag fell into a stocking that had been hung by the fire to dry! This was repeated later with the second daughter. Finally, determined to discover the person who had given him the money, the father secretly hid by the fire every evening until he caught Nicholas dropping in a bag of gold. Nicholas begged the man to not tell anyone what he had done, because he did not want to bring attention to himself. But soon the news got out and when anyone received a secret gift, it was thought that maybe it was from Nicholas.
The Feast Day of St. Nicholas is December 6th. This is the day the Church officially remembers "Santa" and is a good day to give someone a gift - especially if you have children. As you do, you can share the story of the giving spirit of St. Nicholas - and it is that spirit which lives on in Santa Claus and the giving/receiving of gifts as we celebrate the greatest gift of all, the gift of our redemption as we celebrate the Christ Mass on Christmas morning. Yes Virginia, there IS a Santa Claus...