WASHINGTON—President Joe Biden and First Lady Jill Biden brought some Christmas Eve cheer to hospitalized children who aren’t well enough to go home for the holidays. It’s a longstanding tradition for first ladies to visit Children’s National Hospital at Christmastime, but Joe Biden’s visit on Friday was a surprise. It marked the first time that a sitting president had joined the fun, the White House said. It wasn’t the only tradition that the president joined in on Friday. Jill Biden answered calls to the the North American Aerospace Defense Command’s Santa tracking service, another longstanding tradition for first ladies, and she was joined by Biden for the calls. At the hospital, the Bidens spoke with a group of children making lanterns as part of a winter craft project, asking each one what they drew on their lanterns. Some drew family, snowmen or other holiday-themed art. They both spoke to a …