[kulbabka]

получилось

function blocksByChildrenTest(){
		var elements = document.getElementById('list-holder').children;
		var boxes = [];
		for(var i = 0; i < elements.length; i++){
			boxes.push(elements[i].clientHeight);
		}
		var maxHeight = Math.max.apply(null, boxes);
		for (var j = 0; j < elements.length; j++){
			elements[j].style.height = maxHeight + 'px';	
		}
	}
	
	blocksByChildrenTest();