KYIV — A day of mourning has been declared in Kyiv after the second biggest aerial attack of the war so far killed at least 23 people, including four children.The city’s mayor, Vitali Klitschko,KYIV — A day of mourning has been declared in Kyiv after the second biggest aerial attack of the war so far killed at least 23 people, including four children.The city’s mayor, Vitali Klitschko,