When is it a good time to tell children that Santa is not real?

We tried to keep up the Santa traditions as long as possible! YOu know, boot prints on the hearth, leaving the milk half drunk by Santa, and a bite fo cookie left, leaving unwrapped gifts and candy in the stockings...etc. Then, when the children started talking with other kids, who "knew" Santa wasn't real, we decided to come clean. But in a way that helps to preserve the "original" Saint Nicholas story. We told them that there was a Saint Nicholas...but that he was no longer living, and to preserve his memory and good will toward men (and children) people tried to do as Saint Nicholas would dom bringing gifts to others...and obviously that is why there are Santas at every department store. The magic was there...and the legend remains intact forever.