1. override
void removeChildAt(int index)

Source

@override
void removeChildAt(int index) {
  if (index < 0 || index >= _children.length) {
    throw new ArgumentError("The supplied index is out of bounds.");
  } else {
    Bitmap child = _children[index];
    child._parent = null;
    _children.removeAt(index);
  }
}