code: public void addChild(AccessibilityNodeInfo child) {
      if (children == null) {
        children = new ArrayList<>();
      }
  
      children.add(child);
      ShadowAccessibilityNodeInfo shadowAccessibilityNodeInfo = Shadow.extract(child);
      shadowAccessibilityNodeInfo.parent = realAccessibilityNodeInfo;
    }
docs: Add a child node to this one. Also initializes the parent field of the
  child.
  
  @param child The node to be added as a child.