Naomi Watts and Liev Schreiber’s kids have gotten into the “Elf on a Shelf” craze. “I think they are getting into the whole Santa Claus thing,” Watts said of her two sons at the New 42nd Street Gala at the New Victory Theater. “They’ve got the whole ‘Elf on the Shelf’ thing, and every time he moves, they get excited.” We reported on the “Elf” game which helps keeps tabs on who’s been naughty or nice after “GMA” nearly gave away its “magic” secrets to kiddie viewers.