docs: public void addChild( LockedObject newChild ) {
          if (children == null) {
              children = new LockedObject[0];
          }
          int size = children.length;
          LockedObject[] newChildren = new LockedObject[size + 1];
          System.arraycopy(children, 0, newChildren, 0, size);
          newChildren[size] = newChild;
          children = newChildren;
      }