When our first child was born, we started a tradition of buying a special ornament each year for her. As we began decorating the tree, the first ornament that went up was the new one. We made a big deal out of presenting the special ornament. She liked ballerinas so every year she gets a special ballerina ornament.
This tradition has carried on as we had more children.
My oldest son loved trains, so each year he gets a train ornament.