$("#ddlTest_I").kendoComboBox({
        dataTextField: "parentName",
        dataValueField: "parentId",
        dataSource: [
                { parentName: "Parent1", parentId: 1, childName: "Child1", childId: 1 },
                { parentName: "Parent2", parentId: 2, childName: "Child2", childId: 2 },
                { parentName: "Parent1", parentId: 1, childName: "Child3", childId: 3 },
                { parentName: "Parent2", parentId: 2, childName: "Child4", childId: 4 },
                { parentName: "Parent1", parentId: 1, childName: "Child5", childId: 5 }
            ]
    });

$("#ddlTest_II").kendoComboBox({
        cascadeFrom: "ddlTest_I",
        dataTextField: "childName",
        dataValueField: "childId",
        dataSource: [
                {parentName: "Parent1", parentId: 1, childName: "Child1", childId: 1 },
                { parentName: "Parent2", parentId: 2, childName: "Child2", childId: 2 },
                { parentName: "Parent1", parentId: 1, childName: "Child3", childId: 3 },
                { parentName: "Parent2", parentId: 2, childName: "Child4", childId: 4 },
                { parentName: "Parent1", parentId: 1, childName: "Child5", childId: 5 }
            ]
    });

var comboDataSource = new kendo.data.DataSource(parentDatasource.data()); // pseudo
comboDataSource.add(parentDatasource.data()[0]); // might need add item by item