The Day Santa Stopped Believing In Harold by Maureen Fergus
Santa has a problem. This kid? Harold? Santa doesn't think he's real. He WANTS to believe in Harold - after all, Harold is one of the most magical parts of Christmas. Getting Harold's letters, eating the cookies he leaves out, feeding his carrots to the reindeer... what would Christmas be without that? But Santa's just not sure. Some of his friends are telling him they think Harold's not real...