Our only child is in utero at the moment, but we do not plan on doing Santa either.
We plan on celebrating the Feast of St. Nicholas, similar to what was posted above. Also, celebrating the other big feast days in December (Immaculate Conception, O.L Guadalupe, etc) because we generally celebrate feast days around the year (anything for a par-tay

). Also, I think the Swedish custom of celebrating the Feast of St. Lucia (St. Lucy) is interesting, and when we have daughter we may do that one as well…I’ll need to research it more.
For Christmas Eve we’ll decorate the tree and the house, and we’ll keep gifts to a minimum, and encourage each of our children to give a birthday present to Jesus ( I know a family who does this and I love it…their kids either paint a picture, sing in the choir for a Christmas Mass, etc). And of course lots of feasting, reading the Nativity accounts, and in general celebrating the arrival of Our Saviour

Also my parents always made sure that we did some kind of act of charity as a family, like going to help out at a Christmas event for those who are less fortunate, etc.