Many families enjoy the tradition of adding a special ornament for each child to the tree, yearly. My cousin's family followed this through the years, and as each child married and left home, they had many years' worth of Christmas ornaments to take into their new home.
Some families don't do this, but if you want to add some special ornaments here and there, and create a fun tradition in the process, how about a 12 days of Ornaments activity, during the 12 days leading up to Christmas.
Perhaps you will add a single purchased ornament each day. Perhaps you will have the kids construct handmade ornaments each day. Perhaps you will purchase a special collection of ornaments that convey the Christmas story. Perhaps you will add literal 12 Days of Christmas ornaments, representing the 12 Days song. However you fit Christmas ornaments into your activity, take time each of the days, leading up to Christmas, and come together as a family to add the decorations to the tree.