const array = [{
    cantDelete: false,
    cantShifLeft: true,
    cantShiftDown: false,
    cantShiftRight: true,
    cantShiftUp: true,
    children: ["g12034c6b772_0_5", "g12034c6b772_0_25", "g12034c6b772_0_15"],
    displayId: "1",
    id: "533c1e97-465e-4f3e-827b-3b6db8e745f4",
    idx: 0,
    kind: "folder",
    order: 1,
    parent: null,
    title: "test"
  },
  {
    id: "g12034c6b772_0_5",
    kind: "slide",
    notes: "",
    order: 1,
    render: {},
    title: "Slide 1",
    type: "snapshot",
    videos: []
  },
  {
    id: "g12034c6b772_0_25",
    kind: "slide",
    notes: "",
    order: 2,
    render: {},
    title: "Slide 2",
    type: "snapshot",
    videos: []
  },
  {
    id: "g12034c6b772_0_15",
    kind: "slide",
    notes: "",
    order: 3,
    render: {},
    title: "Slide 3",
    type: "snapshot",
    videos: []
  },
  {
    id: "g12034c6b772_0_35",
    kind: "slide",
    notes: "",
    order: 1,
    render: {},
    title: "Slide 1",
    type: "snapshot",
    videos: []
  }
];


function find(array, id) {
  return array.find((obj) => obj.id == id);
}

function extract(array, id) {
  var obj = find(array, id);
  array.splice(array.indexOf(obj), 1);
  return obj;
}


function compact(array) {
  array.forEach(function(item) {
    if (item.kind == "folder") {
      var children = [];
      item.children.forEach(function(id) {
        children.push(extract(array, id));
      })
      item.children = children;
    }
  })
  return array;
}

console.log(compact(array))

.as-console-wrapper {
  max-height: 100% !important;
}