public function addChild($child, array $options = array())
{
if (!$child instanceof ItemInterface) {
$child = $this->factory->createItem($child, $options);
} elseif (null !== $child->getParent()) {
throw new \InvalidArgumentException('Cannot add menu item as child, it already belongs to another menu (e.g. has a parent).');
}
$child->setParent($this);
$this->children[$child->getName()] = $child;
return $child;
}
