Arthur

Arthur is the son of Santa Claus, Mrs. Claus, and the younger brother of Steve Claus. He is very clumsy and is scared of everything. He wears holiday Christmas sweaters and slippers. But he is determined to deliver the present to Gwen no matter what happens to him on the way to Trelew England.

Trivia
During the film there have been a lot of foreshadowings and hints that Arthur will be the next Santa Claus:
 * Arthur's personality shows us that he is kind, caring, brave, truthful and unselfish, which are coincidentally are the traits that Santa Claus is supposed to have.
 * During the dinner scene, Arthur is the only one at the table seen wearing a paper crown. Which of course; wearing a crown symbols the monarch or by a deity, for whom the crown traditionally represents power, legitimacy, victory, triumph, honor, and glory.
 * In the sled barn, when Grandsanta introduces the great great granchildren of the original eight reindeer to Arthur, they all went straight to Arthur, sensing he is Santa Claus.
 * During the ride on Eve, Grandsanta tells Arthur that "every young heir to the Pole gets to take out by his father".
 * Before Eve gets blown up by the military, Arthur was the one who rode on the sleigh.
 * During watching the sleigh barn's security video, Steve slams his espresso cup with the Christmas tree logo under the freeze frame of Arthur holding Gwen's present, hinting that Arthur will be the one to deliver the gift.