Former US president Barack Obama took on a new high-profile role as Father Christmas on Wednesday for a surprise visit to sick children in Washington. Sporting a festive Santa hat and armed with a sack of gifts, he delighted young patients at Children's National hospital with gifts and hugs. In a video he shared on his Twitter account, he is seen telling staff who greeted him with rousing cheers: "I just want to say thank you to all of you guys."