More than 400,000 children in Lebanon have been displaced in the past three weeks, a top official with the UN children’s agency said Monday, warning of a “lost generation” in the small country grappling with multiple crises and now in the middle of war. Israel has escalated its campaign against Lebanon-based Hezbollah, including launching a ground invasion, after a year of exchanges of fire during its war with Hamas in Gaza. The fighting in Lebanon has displaced 1.2 million people from their homes, most of them fleeing to Beirut and elsewhere in the north over the past three weeks since the es…