This feast is often confused with the Annunciation. In fact, David colored a picture of the Annunciation in school today (although he also went to mass where our pastor clearly differentiated between the two events). Maybe it is because we have a good story to go along with that event of the Angel Gabriel coming to see Mary to tell her that she was to become the mother of Jesus. But the Immaculate Conception refers to Mary's conception in the womb of her mother, St. Anne. While Mary was certainly conceived via traditional means, we believe that she was conceived without original sin, that tendency to do wrong that the rest of us are born with.
Still the two events are connected. Mary was conceived without sin precisely because she was someday going to be the mother of Jesus. It was all part of the plan. Just for the record, though, we celebrate the Annunciation on March 25 - nine months before Christmas, and we celebrate Mary's birthday September 8, nine months from today.
Speaking of Mary, however, I wonder if she ever found parenting to be a complete mystery. Jesus was obviously not your run-of-the-mill boy. I wonder if she ever thought to herself, "Just what exactly am I supposed to do with him?" I wonder if she had to struggle to figure it out like the rest of us do.